From: Rob Clark robdclark@chromium.org
This series adds deadline awareness to fences, so realtime deadlines such as vblank can be communicated to the fence signaller for power/ frequency management decisions.
This is partially inspired by a trick i915 does, but implemented via dma-fence for a couple of reasons:
1) To continue to be able to use the atomic helpers 2) To support cases where display and gpu are different drivers
This iteration adds a dma-fence ioctl to set a deadline (both to support igt-tests, and compositors which delay decisions about which client buffer to display), and a sw_sync ioctl to read back the deadline. IGT tests utilizing these can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v1: https://patchwork.freedesktop.org/series/93035/ v2: Move filtering out of later deadlines to fence implementation to avoid increasing the size of dma_fence v3: Add support in fence-array and fence-chain; Add some uabi to support igt tests and userspace compositors. v4: Rebase, address various comments, and add syncobj deadline support, and sync_file EPOLLPRI based on experience with perf/ freq issues with clvk compute workloads on i915 (anv)
Rob Clark (14): dma-buf/dma-fence: Add deadline awareness dma-buf/fence-array: Add fence deadline support dma-buf/fence-chain: Add fence deadline support dma-buf/dma-resv: Add a way to set fence deadline dma-buf/sync_file: Add SET_DEADLINE ioctl dma-buf/sync_file: Support (E)POLLPRI dma-buf/sw_sync: Add fence deadline support drm/scheduler: Add fence deadline support drm/syncobj: Add deadline support for syncobj waits drm/vblank: Add helper to get next vblank time drm/atomic-helper: Set fence deadline for vblank drm/msm: Add deadline based boost support drm/msm: Add wait-boost support drm/i915: Add deadline based boost support
drivers/dma-buf/dma-fence-array.c | 11 ++++ drivers/dma-buf/dma-fence-chain.c | 13 +++++ drivers/dma-buf/dma-fence.c | 20 +++++++ drivers/dma-buf/dma-resv.c | 19 +++++++ drivers/dma-buf/sw_sync.c | 58 +++++++++++++++++++ drivers/dma-buf/sync_debug.h | 2 + drivers/dma-buf/sync_file.c | 27 +++++++++ drivers/gpu/drm/drm_atomic_helper.c | 36 ++++++++++++ drivers/gpu/drm/drm_ioctl.c | 3 + drivers/gpu/drm/drm_syncobj.c | 59 ++++++++++++++++---- drivers/gpu/drm/drm_vblank.c | 32 +++++++++++ drivers/gpu/drm/i915/i915_driver.c | 2 +- drivers/gpu/drm/i915/i915_request.c | 20 +++++++ drivers/gpu/drm/msm/msm_drv.c | 16 ++++-- drivers/gpu/drm/msm/msm_fence.c | 74 +++++++++++++++++++++++++ drivers/gpu/drm/msm/msm_fence.h | 20 +++++++ drivers/gpu/drm/msm/msm_gem.c | 5 ++ drivers/gpu/drm/scheduler/sched_fence.c | 46 +++++++++++++++ drivers/gpu/drm/scheduler/sched_main.c | 2 +- include/drm/drm_drv.h | 6 ++ include/drm/drm_vblank.h | 1 + include/drm/gpu_scheduler.h | 8 +++ include/linux/dma-fence.h | 20 +++++++ include/linux/dma-resv.h | 2 + include/uapi/drm/drm.h | 16 +++++- include/uapi/drm/msm_drm.h | 14 ++++- include/uapi/linux/sync_file.h | 22 ++++++++ 27 files changed, 532 insertions(+), 22 deletions(-)
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com --- drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+ +/** + * dma_fence_set_deadline - set desired fence-wait deadline + * @fence: the fence that is to be waited on + * @deadline: the time by which the waiter hopes for the fence to be + * signaled + * + * Inform the fence signaler of an upcoming deadline, such as vblank, by + * which point the waiter would prefer the fence to be signaled by. This + * is intended to give feedback to the fence signaler to aid in power + * management decisions, such as boosting GPU frequency if a periodic + * vblank deadline is approaching. + */ +void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + if (fence->ops->set_deadline && !dma_fence_is_signaled(fence)) + fence->ops->set_deadline(fence, deadline); +} +EXPORT_SYMBOL(dma_fence_set_deadline); + /** * dma_fence_describe - Dump fence describtion into seq_file * @fence: the 6fence to describe diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, + DMA_FENCE_FLAG_HAS_DEADLINE_BIT, DMA_FENCE_FLAG_USER_BITS, /* must always be last member */ };
@@ -257,6 +258,23 @@ struct dma_fence_ops { */ void (*timeline_value_str)(struct dma_fence *fence, char *str, int size); + + /** + * @set_deadline: + * + * Callback to allow a fence waiter to inform the fence signaler of + * an upcoming deadline, such as vblank, by which point the waiter + * would prefer the fence to be signaled by. This is intended to + * give feedback to the fence signaler to aid in power management + * decisions, such as boosting GPU frequency. + * + * This is called without &dma_fence.lock held, it can be called + * multiple times and from any context. Locking is up to the callee + * if it has some state to manage. + * + * This callback is optional. + */ + void (*set_deadline)(struct dma_fence *fence, ktime_t deadline); };
void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, @@ -583,6 +601,8 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr) return ret < 0 ? ret : 0; }
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline); + struct dma_fence *dma_fence_get_stub(void); struct dma_fence *dma_fence_allocate_private_stub(void); u64 dma_fence_context_alloc(unsigned num);
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
signaled
- Inform the fence signaler of an upcoming deadline, such as vblank, by
- which point the waiter would prefer the fence to be signaled by. This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- if (fence->ops->set_deadline && !dma_fence_is_signaled(fence))
fence->ops->set_deadline(fence, deadline);+} +EXPORT_SYMBOL(dma_fence_set_deadline);
- /**
- dma_fence_describe - Dump fence describtion into seq_file
- @fence: the 6fence to describe
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
- DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
Regards,
Tvrtko
DMA_FENCE_FLAG_USER_BITS, /* must always be last member */ }; @@ -257,6 +258,23 @@ struct dma_fence_ops { */ void (*timeline_value_str)(struct dma_fence *fence, char *str, int size);
- /**
* @set_deadline:** Callback to allow a fence waiter to inform the fence signaler of* an upcoming deadline, such as vblank, by which point the waiter* would prefer the fence to be signaled by. This is intended to* give feedback to the fence signaler to aid in power management* decisions, such as boosting GPU frequency.** This is called without &dma_fence.lock held, it can be called* multiple times and from any context. Locking is up to the callee* if it has some state to manage.** This callback is optional.*/- void (*set_deadline)(struct dma_fence *fence, ktime_t deadline); };
void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, @@ -583,6 +601,8 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr) return ret < 0 ? ret : 0; } +void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
- struct dma_fence *dma_fence_get_stub(void); struct dma_fence *dma_fence_allocate_private_stub(void); u64 dma_fence_context_alloc(unsigned num);
Am 22.02.23 um 11:23 schrieb Tvrtko Ursulin:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout); + +/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
- * signaled
- Inform the fence signaler of an upcoming deadline, such as
vblank, by
- which point the waiter would prefer the fence to be signaled by.
This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + if (fence->ops->set_deadline && !dma_fence_is_signaled(fence)) + fence->ops->set_deadline(fence, deadline); +} +EXPORT_SYMBOL(dma_fence_set_deadline);
/** * dma_fence_describe - Dump fence describtion into seq_file * @fence: the 6fence to describe diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, + DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
I had similar concerns and it took me a moment as well to understand the background why this is necessary. I essentially don't see much other approach we could do.
Yes, this is GPU/CRTC specific, but we somehow need a common interface for communicating it between drivers and that's the dma_fence object as far as I can see.
Regards, Christian.
Regards,
Tvrtko
DMA_FENCE_FLAG_USER_BITS, /* must always be last member */ }; @@ -257,6 +258,23 @@ struct dma_fence_ops { */ void (*timeline_value_str)(struct dma_fence *fence, char *str, int size);
+ /** + * @set_deadline: + * + * Callback to allow a fence waiter to inform the fence signaler of + * an upcoming deadline, such as vblank, by which point the waiter + * would prefer the fence to be signaled by. This is intended to + * give feedback to the fence signaler to aid in power management + * decisions, such as boosting GPU frequency. + * + * This is called without &dma_fence.lock held, it can be called + * multiple times and from any context. Locking is up to the callee + * if it has some state to manage. + * + * This callback is optional. + */ + void (*set_deadline)(struct dma_fence *fence, ktime_t deadline); }; void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, @@ -583,6 +601,8 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr) return ret < 0 ? ret : 0; } +void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
struct dma_fence *dma_fence_get_stub(void); struct dma_fence *dma_fence_allocate_private_stub(void); u64 dma_fence_context_alloc(unsigned num);
On 22/02/2023 15:28, Christian König wrote:
Am 22.02.23 um 11:23 schrieb Tvrtko Ursulin:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout); + +/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
- * signaled
- Inform the fence signaler of an upcoming deadline, such as
vblank, by
- which point the waiter would prefer the fence to be signaled by.
This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + if (fence->ops->set_deadline && !dma_fence_is_signaled(fence)) + fence->ops->set_deadline(fence, deadline); +} +EXPORT_SYMBOL(dma_fence_set_deadline);
/** * dma_fence_describe - Dump fence describtion into seq_file * @fence: the 6fence to describe diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, + DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
I had similar concerns and it took me a moment as well to understand the background why this is necessary. I essentially don't see much other approach we could do.
Yes, this is GPU/CRTC specific, but we somehow need a common interface for communicating it between drivers and that's the dma_fence object as far as I can see.
Yeah I also don't see any other easy options. Just wanted to raise this as something which probably needs some wider acks.
Also what about the "low level" part of my question about the reason, or benefits, of defining the deadline bit in the common layer?
Regards,
Tvrtko
On Wed, Feb 22, 2023 at 9:05 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 22/02/2023 15:28, Christian König wrote:
Am 22.02.23 um 11:23 schrieb Tvrtko Ursulin:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
signaled
- Inform the fence signaler of an upcoming deadline, such as
vblank, by
- which point the waiter would prefer the fence to be signaled by.
This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- if (fence->ops->set_deadline && !dma_fence_is_signaled(fence))
fence->ops->set_deadline(fence, deadline);+} +EXPORT_SYMBOL(dma_fence_set_deadline);
- /**
- dma_fence_describe - Dump fence describtion into seq_file
- @fence: the 6fence to describe
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
- DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
I had similar concerns and it took me a moment as well to understand the background why this is necessary. I essentially don't see much other approach we could do.
Yes, this is GPU/CRTC specific, but we somehow need a common interface for communicating it between drivers and that's the dma_fence object as far as I can see.
Yeah I also don't see any other easy options. Just wanted to raise this as something which probably needs some wider acks.
Also what about the "low level" part of my question about the reason, or benefits, of defining the deadline bit in the common layer?
We could leave DMA_FENCE_FLAG_HAS_DEADLINE_BIT out, but OTOH managing a bitmask that is partially defined in core enum and partially in backend-driver has it's own drawbacks, and it isn't like we are running out of bits.. :shrug:
BR, -R
Regards,
Tvrtko
On 22/02/2023 17:16, Rob Clark wrote:
On Wed, Feb 22, 2023 at 9:05 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 22/02/2023 15:28, Christian König wrote:
Am 22.02.23 um 11:23 schrieb Tvrtko Ursulin:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
signaled
- Inform the fence signaler of an upcoming deadline, such as
vblank, by
- which point the waiter would prefer the fence to be signaled by.
This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- if (fence->ops->set_deadline && !dma_fence_is_signaled(fence))
fence->ops->set_deadline(fence, deadline);+} +EXPORT_SYMBOL(dma_fence_set_deadline);
- /**
- dma_fence_describe - Dump fence describtion into seq_file
- @fence: the 6fence to describe
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
- DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
I had similar concerns and it took me a moment as well to understand the background why this is necessary. I essentially don't see much other approach we could do.
Yes, this is GPU/CRTC specific, but we somehow need a common interface for communicating it between drivers and that's the dma_fence object as far as I can see.
Yeah I also don't see any other easy options. Just wanted to raise this as something which probably needs some wider acks.
Also what about the "low level" part of my question about the reason, or benefits, of defining the deadline bit in the common layer?
We could leave DMA_FENCE_FLAG_HAS_DEADLINE_BIT out, but OTOH managing a bitmask that is partially defined in core enum and partially in backend-driver has it's own drawbacks, and it isn't like we are running out of bits.. :shrug:
There is DMA_FENCE_FLAG_USER_BITS onwards which implementations could use to store their stuff?
And if we skip forward to "drm/scheduler: Add fence deadline support" that's the only place bit is used, right? Would it simply work to look at drm_sched_fence->deadline == 0 as bit not set? Or you see a need to interoperate with other fence implementations via that bit somehow?
Regards,
Tvrtko
On Wed, Feb 22, 2023 at 9:33 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 22/02/2023 17:16, Rob Clark wrote:
On Wed, Feb 22, 2023 at 9:05 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 22/02/2023 15:28, Christian König wrote:
Am 22.02.23 um 11:23 schrieb Tvrtko Ursulin:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+/**
- dma_fence_set_deadline - set desired fence-wait deadline
- @fence: the fence that is to be waited on
- @deadline: the time by which the waiter hopes for the fence to be
signaled
- Inform the fence signaler of an upcoming deadline, such as
vblank, by
- which point the waiter would prefer the fence to be signaled by.
This
- is intended to give feedback to the fence signaler to aid in power
- management decisions, such as boosting GPU frequency if a periodic
- vblank deadline is approaching.
- */
+void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- if (fence->ops->set_deadline && !dma_fence_is_signaled(fence))
fence->ops->set_deadline(fence, deadline);+} +EXPORT_SYMBOL(dma_fence_set_deadline);
- /**
- dma_fence_describe - Dump fence describtion into seq_file
- @fence: the 6fence to describe
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 775cdc0b4f24..d77f6591c453 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -99,6 +99,7 @@ enum dma_fence_flag_bits { DMA_FENCE_FLAG_SIGNALED_BIT, DMA_FENCE_FLAG_TIMESTAMP_BIT, DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
- DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
Would this bit be better left out from core implementation, given how the approach is the component which implements dma-fence has to track the actual deadline and all?
Also taking a step back - are we all okay with starting to expand the relatively simple core synchronisation primitive with side channel data like this? What would be the criteria for what side channel data would be acceptable? Taking note the thing lives outside drivers/gpu/.
I had similar concerns and it took me a moment as well to understand the background why this is necessary. I essentially don't see much other approach we could do.
Yes, this is GPU/CRTC specific, but we somehow need a common interface for communicating it between drivers and that's the dma_fence object as far as I can see.
Yeah I also don't see any other easy options. Just wanted to raise this as something which probably needs some wider acks.
Also what about the "low level" part of my question about the reason, or benefits, of defining the deadline bit in the common layer?
We could leave DMA_FENCE_FLAG_HAS_DEADLINE_BIT out, but OTOH managing a bitmask that is partially defined in core enum and partially in backend-driver has it's own drawbacks, and it isn't like we are running out of bits.. :shrug:
There is DMA_FENCE_FLAG_USER_BITS onwards which implementations could use to store their stuff?
And if we skip forward to "drm/scheduler: Add fence deadline support" that's the only place bit is used, right? Would it simply work to look at drm_sched_fence->deadline == 0 as bit not set? Or you see a need to interoperate with other fence implementations via that bit somehow?
Currently drm/scheduler is the only one using it. I ended up dropping use of it in msm since the deadline is stored in the fence-context instead. But I think it is better to try to avoid assuming that zero means not-set.
It could be moved to drm/sched.. I guess there are few enough implementations at this point to say whether it is something useful to other drivers or not.
BR, -R
Regards,
Tvrtko
On 2023-02-18 16:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling.
v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++ include/linux/dma-fence.h | 20 ++++++++++++++++++++ 2 files changed, 40 insertions(+)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..763b32627684 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -912,6 +912,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count, } EXPORT_SYMBOL(dma_fence_wait_any_timeout);
+/**
The added empty line above creates a problem for scripts/checkpatch.pl--and there's a few others here and there. It'd be a good idea to run this series through checkpatch.pl, if at least informatively.
I wasn't able to apply patch 13 to drm-misc-next or any other known to me branch, and I didn't see base tree information in the cover letter. I skipped it and it compiled okay without it.
From: Rob Clark robdclark@chromium.org
Propagate the deadline to all the fences in the array.
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com --- drivers/dma-buf/dma-fence-array.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c index 5c8a7084577b..9b3ce8948351 100644 --- a/drivers/dma-buf/dma-fence-array.c +++ b/drivers/dma-buf/dma-fence-array.c @@ -123,12 +123,23 @@ static void dma_fence_array_release(struct dma_fence *fence) dma_fence_free(fence); }
+static void dma_fence_array_set_deadline(struct dma_fence *fence, + ktime_t deadline) +{ + struct dma_fence_array *array = to_dma_fence_array(fence); + unsigned i; + + for (i = 0; i < array->num_fences; ++i) + dma_fence_set_deadline(array->fences[i], deadline); +} + const struct dma_fence_ops dma_fence_array_ops = { .get_driver_name = dma_fence_array_get_driver_name, .get_timeline_name = dma_fence_array_get_timeline_name, .enable_signaling = dma_fence_array_enable_signaling, .signaled = dma_fence_array_signaled, .release = dma_fence_array_release, + .set_deadline = dma_fence_array_set_deadline, }; EXPORT_SYMBOL(dma_fence_array_ops);
From: Rob Clark robdclark@chromium.org
Propagate the deadline to all the fences in the chain.
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com for this one. --- drivers/dma-buf/dma-fence-chain.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c index a0d920576ba6..4684874af612 100644 --- a/drivers/dma-buf/dma-fence-chain.c +++ b/drivers/dma-buf/dma-fence-chain.c @@ -206,6 +206,18 @@ static void dma_fence_chain_release(struct dma_fence *fence) dma_fence_free(fence); }
+ +static void dma_fence_chain_set_deadline(struct dma_fence *fence, + ktime_t deadline) +{ + dma_fence_chain_for_each(fence, fence) { + struct dma_fence_chain *chain = to_dma_fence_chain(fence); + struct dma_fence *f = chain ? chain->fence : fence; + + dma_fence_set_deadline(f, deadline); + } +} + const struct dma_fence_ops dma_fence_chain_ops = { .use_64bit_seqno = true, .get_driver_name = dma_fence_chain_get_driver_name, @@ -213,6 +225,7 @@ const struct dma_fence_ops dma_fence_chain_ops = { .enable_signaling = dma_fence_chain_enable_signaling, .signaled = dma_fence_chain_signaled, .release = dma_fence_chain_release, + .set_deadline = dma_fence_chain_set_deadline, }; EXPORT_SYMBOL(dma_fence_chain_ops);
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Propagate the deadline to all the fences in the chain.
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com for this one.
drivers/dma-buf/dma-fence-chain.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c index a0d920576ba6..4684874af612 100644 --- a/drivers/dma-buf/dma-fence-chain.c +++ b/drivers/dma-buf/dma-fence-chain.c @@ -206,6 +206,18 @@ static void dma_fence_chain_release(struct dma_fence *fence) dma_fence_free(fence); }
+static void dma_fence_chain_set_deadline(struct dma_fence *fence,
ktime_t deadline)+{
- dma_fence_chain_for_each(fence, fence) {
struct dma_fence_chain *chain = to_dma_fence_chain(fence);struct dma_fence *f = chain ? chain->fence : fence;
Low level comment - above two lines could be replaced with:
struct dma_fence *f = dma_fence_chain_contained(fence);
Although to be fair I am not sure that wouldn't be making it less readable. From the point of view that fence might not be a chain, so dma_fence_chain_contained() reads a bit dodgy as an API.
Regards,
Tvrtko
dma_fence_set_deadline(f, deadline);- }
+}
- const struct dma_fence_ops dma_fence_chain_ops = { .use_64bit_seqno = true, .get_driver_name = dma_fence_chain_get_driver_name,
@@ -213,6 +225,7 @@ const struct dma_fence_ops dma_fence_chain_ops = { .enable_signaling = dma_fence_chain_enable_signaling, .signaled = dma_fence_chain_signaled, .release = dma_fence_chain_release,
- .set_deadline = dma_fence_chain_set_deadline, }; EXPORT_SYMBOL(dma_fence_chain_ops);
On Wed, Feb 22, 2023 at 2:27 AM Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Propagate the deadline to all the fences in the chain.
Signed-off-by: Rob Clark robdclark@chromium.org Reviewed-by: Christian König christian.koenig@amd.com for this one.
drivers/dma-buf/dma-fence-chain.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c index a0d920576ba6..4684874af612 100644 --- a/drivers/dma-buf/dma-fence-chain.c +++ b/drivers/dma-buf/dma-fence-chain.c @@ -206,6 +206,18 @@ static void dma_fence_chain_release(struct dma_fence *fence) dma_fence_free(fence); }
+static void dma_fence_chain_set_deadline(struct dma_fence *fence,
ktime_t deadline)+{
dma_fence_chain_for_each(fence, fence) {struct dma_fence_chain *chain = to_dma_fence_chain(fence);struct dma_fence *f = chain ? chain->fence : fence;Low level comment - above two lines could be replaced with:
struct dma_fence *f = dma_fence_chain_contained(fence);Although to be fair I am not sure that wouldn't be making it less readable. From the point of view that fence might not be a chain, so dma_fence_chain_contained() reads a bit dodgy as an API.
It does seem to be the canonical way to do it since 18f5fad275ef ("dma-buf: add dma_fence_chain_contained helper").. looks like I missed that when I rebased. I guess for consistency it's best that I use the helper.
BR, -R
Regards,
Tvrtko
dma_fence_set_deadline(f, deadline);}+}
- const struct dma_fence_ops dma_fence_chain_ops = { .use_64bit_seqno = true, .get_driver_name = dma_fence_chain_get_driver_name,
@@ -213,6 +225,7 @@ const struct dma_fence_ops dma_fence_chain_ops = { .enable_signaling = dma_fence_chain_enable_signaling, .signaled = dma_fence_chain_signaled, .release = dma_fence_chain_release,
.set_deadline = dma_fence_chain_set_deadline,
From: Rob Clark robdclark@chromium.org
Add a way to set a deadline on remaining resv fences according to the requested usage.
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/dma-buf/dma-resv.c | 19 +++++++++++++++++++ include/linux/dma-resv.h | 2 ++ 2 files changed, 21 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 1c76aed8e262..0c86f6d577ab 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -684,6 +684,25 @@ long dma_resv_wait_timeout(struct dma_resv *obj, enum dma_resv_usage usage, } EXPORT_SYMBOL_GPL(dma_resv_wait_timeout);
+/** + * dma_resv_set_deadline - Set a deadline on reservation's objects fences + * @obj: the reservation object + * @usage: controls which fences to include, see enum dma_resv_usage. + * @deadline: the requested deadline (MONOTONIC) + */ +void dma_resv_set_deadline(struct dma_resv *obj, enum dma_resv_usage usage, + ktime_t deadline) +{ + struct dma_resv_iter cursor; + struct dma_fence *fence; + + dma_resv_iter_begin(&cursor, obj, usage); + dma_resv_for_each_fence_unlocked(&cursor, fence) { + dma_fence_set_deadline(fence, deadline); + } + dma_resv_iter_end(&cursor); +} +EXPORT_SYMBOL_GPL(dma_resv_set_deadline);
/** * dma_resv_test_signaled - Test if a reservation object's fences have been diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index 0637659a702c..8d0e34dad446 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -479,6 +479,8 @@ int dma_resv_get_singleton(struct dma_resv *obj, enum dma_resv_usage usage, int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src); long dma_resv_wait_timeout(struct dma_resv *obj, enum dma_resv_usage usage, bool intr, unsigned long timeout); +void dma_resv_set_deadline(struct dma_resv *obj, enum dma_resv_usage usage, + ktime_t deadline); bool dma_resv_test_signaled(struct dma_resv *obj, enum dma_resv_usage usage); void dma_resv_describe(struct dma_resv *obj, struct seq_file *seq);
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
Add a way to set a deadline on remaining resv fences according to the requested usage.
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/dma-resv.c | 19 +++++++++++++++++++ include/linux/dma-resv.h | 2 ++ 2 files changed, 21 insertions(+)
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c index 1c76aed8e262..0c86f6d577ab 100644 --- a/drivers/dma-buf/dma-resv.c +++ b/drivers/dma-buf/dma-resv.c @@ -684,6 +684,25 @@ long dma_resv_wait_timeout(struct dma_resv *obj, enum dma_resv_usage usage, } EXPORT_SYMBOL_GPL(dma_resv_wait_timeout); +/**
- dma_resv_set_deadline - Set a deadline on reservation's objects fences
- @obj: the reservation object
- @usage: controls which fences to include, see enum dma_resv_usage.
- @deadline: the requested deadline (MONOTONIC)
Please add an additional description line, something like "Can be called without holding the dma_resv lock and sets @deadline on all fences filtered by @usage.".
With that done the patch is Reviewed-by: Christian König christian.koenig@amd.com
Regards, Christian.
- */
+void dma_resv_set_deadline(struct dma_resv *obj, enum dma_resv_usage usage,
ktime_t deadline)+{
- struct dma_resv_iter cursor;
- struct dma_fence *fence;
- dma_resv_iter_begin(&cursor, obj, usage);
- dma_resv_for_each_fence_unlocked(&cursor, fence) {
dma_fence_set_deadline(fence, deadline);- }
- dma_resv_iter_end(&cursor);
+} +EXPORT_SYMBOL_GPL(dma_resv_set_deadline); /**
- dma_resv_test_signaled - Test if a reservation object's fences have been
diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index 0637659a702c..8d0e34dad446 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -479,6 +479,8 @@ int dma_resv_get_singleton(struct dma_resv *obj, enum dma_resv_usage usage, int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src); long dma_resv_wait_timeout(struct dma_resv *obj, enum dma_resv_usage usage, bool intr, unsigned long timeout); +void dma_resv_set_deadline(struct dma_resv *obj, enum dma_resv_usage usage,
ktime_t deadline);
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; }
+static int sync_file_ioctl_set_deadline(struct sync_file *sync_file, + unsigned long arg) +{ + struct sync_set_deadline ts; + + if (copy_from_user(&ts, (void __user *)arg, sizeof(ts))) + return -EFAULT; + + if (ts.pad) + return -EINVAL; + + dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec)); + + return 0; +} + static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
+ case SYNC_IOC_SET_DEADLINE: + return sync_file_ioctl_set_deadline(sync_file, arg); + default: return -ENOTTY; } diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; };
+/** + * struct sync_set_deadline - set a deadline on a fence + * @tv_sec: seconds elapsed since epoch + * @tv_nsec: nanoseconds elapsed since the time given by the tv_sec + * @pad: must be zero + * + * The timebase for the deadline is CLOCK_MONOTONIC (same as vblank) + */ +struct sync_set_deadline { + __s64 tv_sec; + __s32 tv_nsec; + __u32 pad; +}; + #define SYNC_IOC_MAGIC '>'
/** @@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+ +/** + * DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence + * + * Allows userspace to set a deadline on a fence, see dma_fence_set_deadline() + */ +#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline) + #endif /* _UAPI_LINUX_SYNC_H */
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; } +static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
unsigned long arg)+{
- struct sync_set_deadline ts;
- if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))
return -EFAULT;- if (ts.pad)
return -EINVAL;- dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));
- return 0;
+}
- static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
@@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
- case SYNC_IOC_SET_DEADLINE:
return sync_file_ioctl_set_deadline(sync_file, arg);- default: return -ENOTTY; }
diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; }; +/**
- struct sync_set_deadline - set a deadline on a fence
- @tv_sec: seconds elapsed since epoch
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
- @pad: must be zero
- The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
- */
+struct sync_set_deadline {
- __s64 tv_sec;
- __s32 tv_nsec;
- __u32 pad;
IIRC struct timespec defined this as time_t/long (which is horrible for an UAPI because of the sizeof(long) dependency), one possible alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is essentially ktime).
Not 100% sure if there is any preferences documented, but I think the later might be better.
Either way the patch is Acked-by: Christian König christian.koenig@amd.com for this patch.
Regards, Christian.
+};
- #define SYNC_IOC_MAGIC '>'
/** @@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+/**
- DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
- Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
- */
+#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
- #endif /* _UAPI_LINUX_SYNC_H */
On Mon, Feb 20, 2023 at 12:27 AM Christian König christian.koenig@amd.com wrote:
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; }
+static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
unsigned long arg)+{
struct sync_set_deadline ts;if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))return -EFAULT;if (ts.pad)return -EINVAL;dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));return 0;+}
- static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
@@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
case SYNC_IOC_SET_DEADLINE:return sync_file_ioctl_set_deadline(sync_file, arg);default: return -ENOTTY; }diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; };
+/**
- struct sync_set_deadline - set a deadline on a fence
- @tv_sec: seconds elapsed since epoch
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
- @pad: must be zero
- The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
- */
+struct sync_set_deadline {
__s64 tv_sec;__s32 tv_nsec;__u32 pad;IIRC struct timespec defined this as time_t/long (which is horrible for an UAPI because of the sizeof(long) dependency), one possible alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is essentially ktime).
Not 100% sure if there is any preferences documented, but I think the later might be better.
The original thought is that this maps directly to clock_gettime() without extra conversion needed, and is similar to other pre-ktime_t UAPI. But OTOH if userspace wants to add an offset, it is maybe better to convert completely to ns in userspace and use a u64 (as that is what ns_to_ktime() uses).. (and OFC whatever decision here also applies to the syncobj wait ioctls)
I'm leaning towards u64 CLOCK_MONOTONIC ns if no one has a good argument against that.
BR, -R
Either way the patch is Acked-by: Christian König christian.koenig@amd.com for this patch.
Regards, Christian.
+};
#define SYNC_IOC_MAGIC '>'
/**
@@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+/**
- DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
- Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
- */
+#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
- #endif /* _UAPI_LINUX_SYNC_H */
On Mon, 20 Feb 2023 08:09:04 -0800 Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 20, 2023 at 12:27 AM Christian König christian.koenig@amd.com wrote:
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; }
+static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
unsigned long arg)+{
struct sync_set_deadline ts;if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))return -EFAULT;if (ts.pad)return -EINVAL;dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));return 0;+}
- static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
@@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
case SYNC_IOC_SET_DEADLINE:return sync_file_ioctl_set_deadline(sync_file, arg);default: return -ENOTTY; }diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; };
+/**
- struct sync_set_deadline - set a deadline on a fence
- @tv_sec: seconds elapsed since epoch
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
- @pad: must be zero
- The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
- */
+struct sync_set_deadline {
__s64 tv_sec;__s32 tv_nsec;__u32 pad;IIRC struct timespec defined this as time_t/long (which is horrible for an UAPI because of the sizeof(long) dependency), one possible alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is essentially ktime).
Not 100% sure if there is any preferences documented, but I think the later might be better.
The original thought is that this maps directly to clock_gettime() without extra conversion needed, and is similar to other pre-ktime_t UAPI. But OTOH if userspace wants to add an offset, it is maybe better to convert completely to ns in userspace and use a u64 (as that is what ns_to_ktime() uses).. (and OFC whatever decision here also applies to the syncobj wait ioctls)
I'm leaning towards u64 CLOCK_MONOTONIC ns if no one has a good argument against that.
No, no good argument against that, it's just different from any other UAPI so far, but a new style has to start somewhere. It's good for 584 years after the epoch.
Just make sure the documentation is explicit on how struct timespec is converted to and from u64 (signedness issues, overflow and whatnot).
Thanks, pq
BR, -R
Either way the patch is Acked-by: Christian König christian.koenig@amd.com for this patch.
Regards, Christian.
+};
#define SYNC_IOC_MAGIC '>'
/**
@@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+/**
- DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
- Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
- */
+#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
- #endif /* _UAPI_LINUX_SYNC_H */
Am 20.02.23 um 17:09 schrieb Rob Clark:
On Mon, Feb 20, 2023 at 12:27 AM Christian König christian.koenig@amd.com wrote:
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; }
+static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
unsigned long arg)+{
struct sync_set_deadline ts;if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))return -EFAULT;if (ts.pad)return -EINVAL;dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));return 0;+}
- static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
@@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
case SYNC_IOC_SET_DEADLINE:return sync_file_ioctl_set_deadline(sync_file, arg);default: return -ENOTTY; }diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; };
+/**
- struct sync_set_deadline - set a deadline on a fence
- @tv_sec: seconds elapsed since epoch
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
- @pad: must be zero
- The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
- */
+struct sync_set_deadline {
__s64 tv_sec;__s32 tv_nsec;__u32 pad;IIRC struct timespec defined this as time_t/long (which is horrible for an UAPI because of the sizeof(long) dependency), one possible alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is essentially ktime).
Not 100% sure if there is any preferences documented, but I think the later might be better.
The original thought is that this maps directly to clock_gettime() without extra conversion needed, and is similar to other pre-ktime_t UAPI. But OTOH if userspace wants to add an offset, it is maybe better to convert completely to ns in userspace and use a u64 (as that is what ns_to_ktime() uses).. (and OFC whatever decision here also applies to the syncobj wait ioctls)
I'm leaning towards u64 CLOCK_MONOTONIC ns if no one has a good argument against that.
+1 for that.
Regards, Christian.
BR, -R
Either way the patch is Acked-by: Christian König christian.koenig@amd.com for this patch.
Regards, Christian.
+};
#define SYNC_IOC_MAGIC '>'
/**
@@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+/**
- DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
- Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
- */
+#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
- #endif /* _UAPI_LINUX_SYNC_H */
On Sat, 18 Feb 2023 13:15:48 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
The initial purpose is for igt tests, but this would also be useful for compositors that wait until close to vblank deadline to make decisions about which frame to show.
The igt tests can be found at:
https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadli...
v2: Clarify the timebase, add link to igt tests
Signed-off-by: Rob Clark robdclark@chromium.org
drivers/dma-buf/sync_file.c | 19 +++++++++++++++++++ include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++ 2 files changed, 41 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index af57799c86ce..fb6ca1032885 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -350,6 +350,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, return ret; } +static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
unsigned long arg)+{
- struct sync_set_deadline ts;
- if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))
return -EFAULT;- if (ts.pad)
return -EINVAL;- dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));
- return 0;
+}
static long sync_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -362,6 +378,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd, case SYNC_IOC_FILE_INFO: return sync_file_ioctl_fence_info(sync_file, arg);
- case SYNC_IOC_SET_DEADLINE:
return sync_file_ioctl_set_deadline(sync_file, arg);- default: return -ENOTTY; }
diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h index ee2dcfb3d660..c8666580816f 100644 --- a/include/uapi/linux/sync_file.h +++ b/include/uapi/linux/sync_file.h @@ -67,6 +67,20 @@ struct sync_file_info { __u64 sync_fence_info; }; +/**
- struct sync_set_deadline - set a deadline on a fence
- @tv_sec: seconds elapsed since epoch
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
Hi,
should tv_sec,tv_nsec be validated like clock_settime() does?
It requires: - tv_sec >= 0 - tv_nsec >= 0 - tv_nsec < 1e9
Thanks, pq
- @pad: must be zero
- The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
- */
+struct sync_set_deadline {
- __s64 tv_sec;
- __s32 tv_nsec;
- __u32 pad;
+};
#define SYNC_IOC_MAGIC '>' /** @@ -95,4 +109,12 @@ struct sync_file_info { */ #define SYNC_IOC_FILE_INFO _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
+/**
- DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
- Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
- */
+#define SYNC_IOC_SET_DEADLINE _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
#endif /* _UAPI_LINUX_SYNC_H */
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
+ /* + * The POLLPRI/EPOLLPRI flag can be used to signal that + * userspace wants the fence to signal ASAP, express this + * as an immediate deadline. + */ + if (poll_requested_events(wait) & EPOLLPRI) + dma_fence_set_deadline(sync_file->fence, ktime_get()); + poll_wait(file, &sync_file->wq, wait);
if (list_empty(&sync_file->cb.node) &&
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
The code looks clean, but the different poll flags and their meaning are certainly not my field of expertise.
Feel free to add Acked-by: Christian König christian.koenig@amd.com, somebody with more background in this should probably take a look as well.
Regards, Christian.
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
- /*
* The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/- if (poll_requested_events(wait) & EPOLLPRI)
dma_fence_set_deadline(sync_file->fence, ktime_get());- poll_wait(file, &sync_file->wq, wait);
if (list_empty(&sync_file->cb.node) &&
On Mon, 20 Feb 2023 09:31:41 +0100 Christian König christian.koenig@amd.com wrote:
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
The code looks clean, but the different poll flags and their meaning are certainly not my field of expertise.
A good question. epoll_ctl manual refers to poll(2) which says:
POLLPRI There is some exceptional condition on the file descriptor. Possibilities include:
• There is out-of-band data on a TCP socket (see tcp(7)).
• A pseudoterminal master in packet mode has seen a state change on the slave (see ioctl_tty(2)).
• A cgroup.events file has been modified (see cgroups(7)).
It seems to be about selecting what events will trigger the poll, more than how (fast) to poll. At least it is not documented to be ignored in 'events', so I guess it should work.
Thanks, pq
Feel free to add Acked-by: Christian König christian.koenig@amd.com, somebody with more background in this should probably take a look as well.
Regards, Christian.
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
- /*
* The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/- if (poll_requested_events(wait) & EPOLLPRI)
dma_fence_set_deadline(sync_file->fence, ktime_get());- poll_wait(file, &sync_file->wq, wait);
if (list_empty(&sync_file->cb.node) &&
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
Thanks, pq
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
- /*
* The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/- if (poll_requested_events(wait) & EPOLLPRI)
dma_fence_set_deadline(sync_file->fence, ktime_get());- poll_wait(file, &sync_file->wq, wait);
if (list_empty(&sync_file->cb.node) &&
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
BR, -R
Thanks, pq
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
/** The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/if (poll_requested_events(wait) & EPOLLPRI)dma_fence_set_deadline(sync_file->fence, ktime_get());poll_wait(file, &sync_file->wq, wait); if (list_empty(&sync_file->cb.node) &&
On Mon, 20 Feb 2023 08:14:47 -0800 Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Sounds good. Docs... ;-)
Hmm, so a compositor should set the deadline when it processes the wl_surface.commit, and not when it actually starts repainting, to give time for the driver to react and the GPU to do some more work. The deadline would be the time when the compositor starts its repaint, so it knows if the buffer is ready or not.
Thanks, pq
BR, -R
Thanks, pq
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
/** The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/if (poll_requested_events(wait) & EPOLLPRI)dma_fence_set_deadline(sync_file->fence, ktime_get());poll_wait(file, &sync_file->wq, wait); if (list_empty(&sync_file->cb.node) &&
On Tue, Feb 21, 2023 at 9:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 20 Feb 2023 08:14:47 -0800 Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Sounds good. Docs... ;-)
Hmm, so a compositor should set the deadline when it processes the wl_surface.commit, and not when it actually starts repainting, to give time for the driver to react and the GPU to do some more work. The deadline would be the time when the compositor starts its repaint, so it knows if the buffer is ready or not.
Technically we don't know when the commit is supposed to be shown. Just passing a deadline of the next possible deadline however is probably a good enough guess for this feature to be useful.
One thing that neither API allows us to do is tell the kernel in advance when we're going to submit work and what the deadline for it is and unfortunately that work is the most timing sensitive.
Thanks, pq
BR, -R
Thanks, pq
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
/** The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/if (poll_requested_events(wait) & EPOLLPRI)dma_fence_set_deadline(sync_file->fence, ktime_get());poll_wait(file, &sync_file->wq, wait); if (list_empty(&sync_file->cb.node) &&
On Tue, Feb 21, 2023 at 8:01 AM Sebastian Wick sebastian.wick@redhat.com wrote:
On Tue, Feb 21, 2023 at 9:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Mon, 20 Feb 2023 08:14:47 -0800 Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Sounds good. Docs... ;-)
Hmm, so a compositor should set the deadline when it processes the wl_surface.commit, and not when it actually starts repainting, to give time for the driver to react and the GPU to do some more work. The deadline would be the time when the compositor starts its repaint, so it knows if the buffer is ready or not.
Technically we don't know when the commit is supposed to be shown. Just passing a deadline of the next possible deadline however is probably a good enough guess for this feature to be useful.
One thing that neither API allows us to do is tell the kernel in advance when we're going to submit work and what the deadline for it is and unfortunately that work is the most timing sensitive.
Presumably you are talking about the final compositing step? Elsewhere in this series that atomic wait-for-fences step sets the deadline hint.
BR, -R
Thanks, pq
BR, -R
Thanks, pq
drivers/dma-buf/sync_file.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index fb6ca1032885..c30b2085ee0a 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait) { struct sync_file *sync_file = file->private_data;
/** The POLLPRI/EPOLLPRI flag can be used to signal that* userspace wants the fence to signal ASAP, express this* as an immediate deadline.*/if (poll_requested_events(wait) & EPOLLPRI)dma_fence_set_deadline(sync_file->fence, ktime_get());poll_wait(file, &sync_file->wq, wait); if (list_empty(&sync_file->cb.node) &&
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
BR, -R
On Tue, 21 Feb 2023 09:53:56 -0800 Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
In that case, I would be conservative, and not add the POLLPRI semantics. An UAPI addition that is not strictly needed and somewhat unclear if it violates any design principles is best not done, until it is proven to be beneficial.
Besides, a Wayland compositor does not necessary need to add the fd to its main event loop for poll. It could just SET_DEADLINE, and then when it renders simply check if the fence passed or not already. Not polling means the compositor does not need to wake up at the moment the fence signals to just record a flag.
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
Maybe it's a soft-realtime app whose primary goal is not display, and it needs the result faster than the window server?
Maybe SET_DEADLINE should set the deadline only to an earlier timestamp and never later?
Thanks, pq
On 2023-02-22 04:49, Pekka Paalanen wrote:
On Tue, 21 Feb 2023 09:53:56 -0800 Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
In that case, I would be conservative, and not add the POLLPRI semantics. An UAPI addition that is not strictly needed and somewhat unclear if it violates any design principles is best not done, until it is proven to be beneficial.
That is my sentiment as well. Moreover, on hard-realtime systems, one would want to set the deadline at the outset and not at poll time.
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 21 Feb 2023 09:53:56 -0800 Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote:
From: Rob Clark robdclark@chromium.org
Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent wait (as opposed to a "housekeeping" wait to know when to cleanup after some work has completed). Usermode components of GPU driver stacks often poll() on fence fd's to know when it is safe to do things like free or reuse a buffer, but they can also poll() on a fence fd when waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag lets the kernel differentiate these two cases.
Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
In that case, I would be conservative, and not add the POLLPRI semantics. An UAPI addition that is not strictly needed and somewhat unclear if it violates any design principles is best not done, until it is proven to be beneficial.
Besides, a Wayland compositor does not necessary need to add the fd to its main event loop for poll. It could just SET_DEADLINE, and then when it renders simply check if the fence passed or not already. Not polling means the compositor does not need to wake up at the moment the fence signals to just record a flag.
poll(POLLPRI) isn't intended for wayland.. but is a thing I want in mesa for fence waits. I _could_ use SET_DEADLINE but it is two syscalls and correspondingly more code ;-)
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
BR, -R
Maybe it's a soft-realtime app whose primary goal is not display, and it needs the result faster than the window server?
Maybe SET_DEADLINE should set the deadline only to an earlier timestamp and never later?
Thanks, pq
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 21 Feb 2023 09:53:56 -0800 Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Sat, 18 Feb 2023 13:15:49 -0800 Rob Clark robdclark@gmail.com wrote: > From: Rob Clark robdclark@chromium.org > > Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent > wait (as opposed to a "housekeeping" wait to know when to cleanup after > some work has completed). Usermode components of GPU driver stacks > often poll() on fence fd's to know when it is safe to do things like > free or reuse a buffer, but they can also poll() on a fence fd when > waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag > lets the kernel differentiate these two cases. > > Signed-off-by: Rob Clark robdclark@chromium.org
Hi,
where would the UAPI documentation of this go? It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
If a Wayland compositor is polling application fences to know which client buffer to use in its rendering, should the compositor poll with PRI or not? If a compositor polls with PRI, then all fences from all applications would always be PRI. Would that be harmful somehow or would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
In that case, I would be conservative, and not add the POLLPRI semantics. An UAPI addition that is not strictly needed and somewhat unclear if it violates any design principles is best not done, until it is proven to be beneficial.
Besides, a Wayland compositor does not necessary need to add the fd to its main event loop for poll. It could just SET_DEADLINE, and then when it renders simply check if the fence passed or not already. Not polling means the compositor does not need to wake up at the moment the fence signals to just record a flag.
poll(POLLPRI) isn't intended for wayland.. but is a thing I want in mesa for fence waits. I _could_ use SET_DEADLINE but it is two syscalls and correspondingly more code ;-)
But is it actually beneficial? "More code" seems quite irrelevant.
Would there be a hundred or more of those per frame? Or would it be always limited to one or two? Or totally depend on what the application is doing? Is it a significant impact?
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
Thanks, pq
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Tue, 21 Feb 2023 09:53:56 -0800 Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 21, 2023 at 8:48 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-20 11:14, Rob Clark wrote:
On Mon, Feb 20, 2023 at 12:53 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > On Sat, 18 Feb 2023 13:15:49 -0800 > Rob Clark robdclark@gmail.com wrote: > >> From: Rob Clark robdclark@chromium.org >> >> Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent >> wait (as opposed to a "housekeeping" wait to know when to cleanup after >> some work has completed). Usermode components of GPU driver stacks >> often poll() on fence fd's to know when it is safe to do things like >> free or reuse a buffer, but they can also poll() on a fence fd when >> waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag >> lets the kernel differentiate these two cases. >> >> Signed-off-by: Rob Clark robdclark@chromium.org > > Hi, > > where would the UAPI documentation of this go? > It seems to be missing.
Good question, I am not sure. The poll() man page has a description, but my usage doesn't fit that _exactly_ (but OTOH the description is a bit vague).
> If a Wayland compositor is polling application fences to know which > client buffer to use in its rendering, should the compositor poll with > PRI or not? If a compositor polls with PRI, then all fences from all > applications would always be PRI. Would that be harmful somehow or > would it be beneficial?
I think a compositor would rather use the deadline ioctl and then poll without PRI. Otherwise you are giving an urgency signal to the fence signaller which might not necessarily be needed.
The places where I expect PRI to be useful is more in mesa (things like glFinish(), readpix, and other similar sorts of blocking APIs)
Hi,
Hmm, but then user-space could do the opposite, namely, submit work as usual--never using the SET_DEADLINE ioctl, and then at the end, poll using (E)POLLPRI. That seems like a possible usage pattern, unintended--maybe, but possible. Do we want to discourage this? Wouldn't SET_DEADLINE be enough? I mean, one can call SET_DEADLINE with the current time, and then wouldn't that be equivalent to (E)POLLPRI?
Yeah, (E)POLLPRI isn't strictly needed if we have SET_DEADLINE. It is slightly more convenient if you want an immediate deadline (single syscall instead of two), but not strictly needed. OTOH it piggy-backs on existing UABI.
In that case, I would be conservative, and not add the POLLPRI semantics. An UAPI addition that is not strictly needed and somewhat unclear if it violates any design principles is best not done, until it is proven to be beneficial.
Besides, a Wayland compositor does not necessary need to add the fd to its main event loop for poll. It could just SET_DEADLINE, and then when it renders simply check if the fence passed or not already. Not polling means the compositor does not need to wake up at the moment the fence signals to just record a flag.
poll(POLLPRI) isn't intended for wayland.. but is a thing I want in mesa for fence waits. I _could_ use SET_DEADLINE but it is two syscalls and correspondingly more code ;-)
But is it actually beneficial? "More code" seems quite irrelevant.
Would there be a hundred or more of those per frame? Or would it be always limited to one or two? Or totally depend on what the application is doing? Is it a significant impact?
In general, any time the CPU is waiting on the GPU, you have already lost. So I don't think the extra syscall is too much of a problem. Just less convenient.
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
BR, -R
Thanks, pq
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
See the topic of implementing triple-buffering in Mutter in order to put more work to the GPU in order to have the GPU ramp up clocks in order to not miss rendering deadlines. I don't think that patch set has landed in Mutter upstream, but I hear distributions in downstream are already carrying it.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1383 https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441
Granted, GPU clocks are just one side of that story it seems, and triple-buffering may have other benefits.
If SET_DEADLINE would fix that problem without triple-buffering, it is definitely userspace observable, expected and eventually required behaviour.
Thanks, pq
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
Regards,
Tvrtko
See the topic of implementing triple-buffering in Mutter in order to put more work to the GPU in order to have the GPU ramp up clocks in order to not miss rendering deadlines. I don't think that patch set has landed in Mutter upstream, but I hear distributions in downstream are already carrying it.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1383 https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1441
Granted, GPU clocks are just one side of that story it seems, and triple-buffering may have other benefits.
If SET_DEADLINE would fix that problem without triple-buffering, it is definitely userspace observable, expected and eventually required behaviour.
Thanks, pq
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
On another matter, if the application uses SET_DEADLINE with one timestamp, and the compositor uses SET_DEADLINE on the same thing with another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
Thanks, pq
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
> On another matter, if the application uses SET_DEADLINE with one > timestamp, and the compositor uses SET_DEADLINE on the same thing with > another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Regards,
Tvrtko
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote: > On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
>> On another matter, if the application uses SET_DEADLINE with one >> timestamp, and the compositor uses SET_DEADLINE on the same thing with >> another timestamp, what should happen? > > The expectation is that many deadline hints can be set on a fence. > The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
Thanks, pq
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > On Wed, 22 Feb 2023 07:37:26 -0800 > Rob Clark robdclark@gmail.com wrote: > >> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
>>> On another matter, if the application uses SET_DEADLINE with one >>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>> another timestamp, what should happen? >> >> The expectation is that many deadline hints can be set on a fence. >> The fence signaller should track the soonest deadline. > > You need to document that as UAPI, since it is observable to userspace. > It would be bad if drivers or subsystems would differ in behaviour. >
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
Regards,
Tvrtko
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote: > On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >> >> On Wed, 22 Feb 2023 07:37:26 -0800 >> Rob Clark robdclark@gmail.com wrote: >> >>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
... >>>> On another matter, if the application uses SET_DEADLINE with one >>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>> another timestamp, what should happen? >>> >>> The expectation is that many deadline hints can be set on a fence. >>> The fence signaller should track the soonest deadline. >> >> You need to document that as UAPI, since it is observable to userspace. >> It would be bad if drivers or subsystems would differ in behaviour. >> > > It is in the end a hint. It is about giving the driver more > information so that it can make better choices. But the driver is > even free to ignore it. So maybe "expectation" is too strong of a > word. Rather, any other behavior doesn't really make sense. But it > could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote: > On Thu, 23 Feb 2023 10:51:48 -0800 > Rob Clark robdclark@gmail.com wrote: > >> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>> >>> On Wed, 22 Feb 2023 07:37:26 -0800 >>> Rob Clark robdclark@gmail.com wrote: >>> >>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > ... > >>>>> On another matter, if the application uses SET_DEADLINE with one >>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>> another timestamp, what should happen? >>>> >>>> The expectation is that many deadline hints can be set on a fence. >>>> The fence signaller should track the soonest deadline. >>> >>> You need to document that as UAPI, since it is observable to userspace. >>> It would be bad if drivers or subsystems would differ in behaviour. >>> >> >> It is in the end a hint. It is about giving the driver more >> information so that it can make better choices. But the driver is >> even free to ignore it. So maybe "expectation" is too strong of a >> word. Rather, any other behavior doesn't really make sense. But it >> could end up being dictated by how the hw and/or fw works. > > It will stop being a hint once it has been implemented and used in the > wild long enough. The kernel userspace regression rules make sure of > that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
BR, -R
-- Regards, Luben
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
> On 24/02/2023 09:26, Pekka Paalanen wrote: >> On Thu, 23 Feb 2023 10:51:48 -0800 >> Rob Clark robdclark@gmail.com wrote: >> >>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>> >>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>> Rob Clark robdclark@gmail.com wrote: >>>> >>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >> >> ... >> >>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>> another timestamp, what should happen? >>>>> >>>>> The expectation is that many deadline hints can be set on a fence. >>>>> The fence signaller should track the soonest deadline. >>>> >>>> You need to document that as UAPI, since it is observable to userspace. >>>> It would be bad if drivers or subsystems would differ in behaviour. >>>> >>> >>> It is in the end a hint. It is about giving the driver more >>> information so that it can make better choices. But the driver is >>> even free to ignore it. So maybe "expectation" is too strong of a >>> word. Rather, any other behavior doesn't really make sense. But it >>> could end up being dictated by how the hw and/or fw works. >> >> It will stop being a hint once it has been implemented and used in the >> wild long enough. The kernel userspace regression rules make sure of >> that. > > Yeah, tricky and maybe a gray area in this case. I think we eluded > elsewhere in the thread that renaming the thing might be an option. > > So maybe instead of deadline, which is a very strong word, use something > along the lines of "present time hint", or "signalled time hint"? Maybe > reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
BR, -R
-- Regards, Luben
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 10:24, Pekka Paalanen wrote: > On Fri, 24 Feb 2023 09:41:46 +0000 > Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > >> On 24/02/2023 09:26, Pekka Paalanen wrote: >>> On Thu, 23 Feb 2023 10:51:48 -0800 >>> Rob Clark robdclark@gmail.com wrote: >>> >>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>> >>>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>>> Rob Clark robdclark@gmail.com wrote: >>>>> >>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>> >>> ... >>> >>>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>>> another timestamp, what should happen? >>>>>> >>>>>> The expectation is that many deadline hints can be set on a fence. >>>>>> The fence signaller should track the soonest deadline. >>>>> >>>>> You need to document that as UAPI, since it is observable to userspace. >>>>> It would be bad if drivers or subsystems would differ in behaviour. >>>>> >>>> >>>> It is in the end a hint. It is about giving the driver more >>>> information so that it can make better choices. But the driver is >>>> even free to ignore it. So maybe "expectation" is too strong of a >>>> word. Rather, any other behavior doesn't really make sense. But it >>>> could end up being dictated by how the hw and/or fw works. >>> >>> It will stop being a hint once it has been implemented and used in the >>> wild long enough. The kernel userspace regression rules make sure of >>> that. >> >> Yeah, tricky and maybe a gray area in this case. I think we eluded >> elsewhere in the thread that renaming the thing might be an option. >> >> So maybe instead of deadline, which is a very strong word, use something >> along the lines of "present time hint", or "signalled time hint"? Maybe >> reads clumsy. Just throwing some ideas for a start. > > You can try, but I fear that if it ever changes behaviour and > someone notices that, it's labelled as a kernel regression. I don't > think documentation has ever been the authoritative definition of UABI > in Linux, it just guides drivers and userspace towards a common > understanding and common usage patterns. > > So even if the UABI contract is not documented (ugh), you need to be > prepared to set the UABI contract through kernel implementation.
To be the devil's advocate it probably wouldn't be an ABI regression but just an regression. Same way as what nice(2) priorities mean hasn't always been the same over the years, I don't think there is a strict contract.
Having said that, it may be different with latency sensitive stuff such as UIs though since it is very observable and can be very painful to users.
> If you do not document the UABI contract, then different drivers are > likely to implement it differently, leading to differing behaviour. > Also userspace will invent wild ways to abuse the UABI if there is no > documentation guiding it on proper use. If userspace or end users > observe different behaviour, that's bad even if it's not a regression. > > I don't like the situation either, but it is what it is. UABI stability > trumps everything regardless of whether it was documented or not. > > I bet userspace is going to use this as a "make it faster, make it > hotter" button. I would not be surprised if someone wrote a LD_PRELOAD > library that stamps any and all fences with an expired deadline to > just squeeze out a little more through some weird side-effect. > > Well, that's hopefully overboard in scaring, but in the end, I would > like to see UABI documented so I can have a feeling of what it is for > and how it was intended to be used. That's all.
We share the same concern. If you read elsewhere in these threads you will notice I have been calling this an "arms race". If the ability to make yourself go faster does not required additional privilege I also worry everyone will do it at which point it becomes pointless. So yes, I do share this concern about exposing any of this as an unprivileged uapi.
Is it possible to limit access to only compositors in some sane way? Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
BR, -R
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
> On 24/02/2023 10:24, Pekka Paalanen wrote: >> On Fri, 24 Feb 2023 09:41:46 +0000 >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: >> >>> On 24/02/2023 09:26, Pekka Paalanen wrote: >>>> On Thu, 23 Feb 2023 10:51:48 -0800 >>>> Rob Clark robdclark@gmail.com wrote: >>>> >>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>>> >>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>>>> Rob Clark robdclark@gmail.com wrote: >>>>>> >>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>> >>>> ... >>>> >>>>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>>>> another timestamp, what should happen? >>>>>>> >>>>>>> The expectation is that many deadline hints can be set on a fence. >>>>>>> The fence signaller should track the soonest deadline. >>>>>> >>>>>> You need to document that as UAPI, since it is observable to userspace. >>>>>> It would be bad if drivers or subsystems would differ in behaviour. >>>>>> >>>>> >>>>> It is in the end a hint. It is about giving the driver more >>>>> information so that it can make better choices. But the driver is >>>>> even free to ignore it. So maybe "expectation" is too strong of a >>>>> word. Rather, any other behavior doesn't really make sense. But it >>>>> could end up being dictated by how the hw and/or fw works. >>>> >>>> It will stop being a hint once it has been implemented and used in the >>>> wild long enough. The kernel userspace regression rules make sure of >>>> that. >>> >>> Yeah, tricky and maybe a gray area in this case. I think we eluded >>> elsewhere in the thread that renaming the thing might be an option. >>> >>> So maybe instead of deadline, which is a very strong word, use something >>> along the lines of "present time hint", or "signalled time hint"? Maybe >>> reads clumsy. Just throwing some ideas for a start. >> >> You can try, but I fear that if it ever changes behaviour and >> someone notices that, it's labelled as a kernel regression. I don't >> think documentation has ever been the authoritative definition of UABI >> in Linux, it just guides drivers and userspace towards a common >> understanding and common usage patterns. >> >> So even if the UABI contract is not documented (ugh), you need to be >> prepared to set the UABI contract through kernel implementation. > > To be the devil's advocate it probably wouldn't be an ABI regression but > just an regression. Same way as what nice(2) priorities mean hasn't > always been the same over the years, I don't think there is a strict > contract. > > Having said that, it may be different with latency sensitive stuff such > as UIs though since it is very observable and can be very painful to users. > >> If you do not document the UABI contract, then different drivers are >> likely to implement it differently, leading to differing behaviour. >> Also userspace will invent wild ways to abuse the UABI if there is no >> documentation guiding it on proper use. If userspace or end users >> observe different behaviour, that's bad even if it's not a regression. >> >> I don't like the situation either, but it is what it is. UABI stability >> trumps everything regardless of whether it was documented or not. >> >> I bet userspace is going to use this as a "make it faster, make it >> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD >> library that stamps any and all fences with an expired deadline to >> just squeeze out a little more through some weird side-effect. >> >> Well, that's hopefully overboard in scaring, but in the end, I would >> like to see UABI documented so I can have a feeling of what it is for >> and how it was intended to be used. That's all. > > We share the same concern. If you read elsewhere in these threads you > will notice I have been calling this an "arms race". If the ability to > make yourself go faster does not required additional privilege I also > worry everyone will do it at which point it becomes pointless. So yes, I > do share this concern about exposing any of this as an unprivileged uapi. > > Is it possible to limit access to only compositors in some sane way? > Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority. We know when there are input events which actually matter. We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
1. The compositor has no way to communicate any of that information to the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
BR, -R
On Mon, Feb 27, 2023 at 2:44 PM Sebastian Wick sebastian.wick@redhat.com wrote:
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote: > On Fri, 24 Feb 2023 10:50:51 +0000 > Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > >> On 24/02/2023 10:24, Pekka Paalanen wrote: >>> On Fri, 24 Feb 2023 09:41:46 +0000 >>> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: >>> >>>> On 24/02/2023 09:26, Pekka Paalanen wrote: >>>>> On Thu, 23 Feb 2023 10:51:48 -0800 >>>>> Rob Clark robdclark@gmail.com wrote: >>>>> >>>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>>>> >>>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>>>>> Rob Clark robdclark@gmail.com wrote: >>>>>>> >>>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>> >>>>> ... >>>>> >>>>>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>>>>> another timestamp, what should happen? >>>>>>>> >>>>>>>> The expectation is that many deadline hints can be set on a fence. >>>>>>>> The fence signaller should track the soonest deadline. >>>>>>> >>>>>>> You need to document that as UAPI, since it is observable to userspace. >>>>>>> It would be bad if drivers or subsystems would differ in behaviour. >>>>>>> >>>>>> >>>>>> It is in the end a hint. It is about giving the driver more >>>>>> information so that it can make better choices. But the driver is >>>>>> even free to ignore it. So maybe "expectation" is too strong of a >>>>>> word. Rather, any other behavior doesn't really make sense. But it >>>>>> could end up being dictated by how the hw and/or fw works. >>>>> >>>>> It will stop being a hint once it has been implemented and used in the >>>>> wild long enough. The kernel userspace regression rules make sure of >>>>> that. >>>> >>>> Yeah, tricky and maybe a gray area in this case. I think we eluded >>>> elsewhere in the thread that renaming the thing might be an option. >>>> >>>> So maybe instead of deadline, which is a very strong word, use something >>>> along the lines of "present time hint", or "signalled time hint"? Maybe >>>> reads clumsy. Just throwing some ideas for a start. >>> >>> You can try, but I fear that if it ever changes behaviour and >>> someone notices that, it's labelled as a kernel regression. I don't >>> think documentation has ever been the authoritative definition of UABI >>> in Linux, it just guides drivers and userspace towards a common >>> understanding and common usage patterns. >>> >>> So even if the UABI contract is not documented (ugh), you need to be >>> prepared to set the UABI contract through kernel implementation. >> >> To be the devil's advocate it probably wouldn't be an ABI regression but >> just an regression. Same way as what nice(2) priorities mean hasn't >> always been the same over the years, I don't think there is a strict >> contract. >> >> Having said that, it may be different with latency sensitive stuff such >> as UIs though since it is very observable and can be very painful to users. >> >>> If you do not document the UABI contract, then different drivers are >>> likely to implement it differently, leading to differing behaviour. >>> Also userspace will invent wild ways to abuse the UABI if there is no >>> documentation guiding it on proper use. If userspace or end users >>> observe different behaviour, that's bad even if it's not a regression. >>> >>> I don't like the situation either, but it is what it is. UABI stability >>> trumps everything regardless of whether it was documented or not. >>> >>> I bet userspace is going to use this as a "make it faster, make it >>> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD >>> library that stamps any and all fences with an expired deadline to >>> just squeeze out a little more through some weird side-effect. >>> >>> Well, that's hopefully overboard in scaring, but in the end, I would >>> like to see UABI documented so I can have a feeling of what it is for >>> and how it was intended to be used. That's all. >> >> We share the same concern. If you read elsewhere in these threads you >> will notice I have been calling this an "arms race". If the ability to >> make yourself go faster does not required additional privilege I also >> worry everyone will do it at which point it becomes pointless. So yes, I >> do share this concern about exposing any of this as an unprivileged uapi. >> >> Is it possible to limit access to only compositors in some sane way? >> Sounds tricky when dma-fence should be disconnected from DRM.. > > Maybe it's not that bad in this particular case, because we are talking > only about boosting GPU clocks which benefits everyone (except > battery life) and it does not penalize other programs like e.g. > job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
> Drivers are not going to use the deadline for scheduling priorities, > right? I don't recall seeing any mention of that. > > ...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
the dynamic double/triple buffer thing?
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority.
This sounds like something orthogonal.. something for cgroups? Ie. android moves visible/foreground apps to a different cgroup to given them higher priority. Tvrtko had a patchset to add drm cgroup support..
We know when there are input events which actually matter.
This I see input as a different boost source for the driver. (Ie. one boost signal is missing fence deadlines, another is input events, etc.)
We end up using downstream input-handlers on the kernel side for this. Partially for the freq boost (but mostly not, UI interactive workloads like touchscreen scrolling don't generally need high GPU freqs, they are more memory bandwidth limited if they are limited by anything).. really the reason here is to get a head-start on the ~2ms that it takes to power up the GPU if it is suspended.
But this is not quite perfect, since for example some keys should be handled on key-down but others on key-up.
But again, this is something different from fence deadlines. I'm interested in proposals because we do need something for this. But I think it is something is orthogonal to this series. For input, we want the kernel to know long before userspace is ready to submit rendering.
We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
- The compositor has no way to communicate any of that information to
the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
If the client isn't using multiple GPUs, a single fence should be sufficient. And even if it is, well we still have all the dependency information on the kernel side. Ie. drm/sched knows what fences it is waiting on if it is waiting to schedule the work associated with the last fence. It would otherwise require drm/sched to be a bit more tricky than it is so far in this series.
But I think the normal dual-gpu case, the app is only dealing with a single GPU?
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
Yeah, I think the thing is you need multiple things, and this is only one of them ;-)
BR, -R
On Tue, Feb 28, 2023 at 12:48 AM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 2:44 PM Sebastian Wick sebastian.wick@redhat.com wrote:
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote: > > On 24/02/2023 11:00, Pekka Paalanen wrote: >> On Fri, 24 Feb 2023 10:50:51 +0000 >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: >> >>> On 24/02/2023 10:24, Pekka Paalanen wrote: >>>> On Fri, 24 Feb 2023 09:41:46 +0000 >>>> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: >>>> >>>>> On 24/02/2023 09:26, Pekka Paalanen wrote: >>>>>> On Thu, 23 Feb 2023 10:51:48 -0800 >>>>>> Rob Clark robdclark@gmail.com wrote: >>>>>> >>>>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>>>>> >>>>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>>>>>> Rob Clark robdclark@gmail.com wrote: >>>>>>>> >>>>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>>> >>>>>> ... >>>>>> >>>>>>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>>>>>> another timestamp, what should happen? >>>>>>>>> >>>>>>>>> The expectation is that many deadline hints can be set on a fence. >>>>>>>>> The fence signaller should track the soonest deadline. >>>>>>>> >>>>>>>> You need to document that as UAPI, since it is observable to userspace. >>>>>>>> It would be bad if drivers or subsystems would differ in behaviour. >>>>>>>> >>>>>>> >>>>>>> It is in the end a hint. It is about giving the driver more >>>>>>> information so that it can make better choices. But the driver is >>>>>>> even free to ignore it. So maybe "expectation" is too strong of a >>>>>>> word. Rather, any other behavior doesn't really make sense. But it >>>>>>> could end up being dictated by how the hw and/or fw works. >>>>>> >>>>>> It will stop being a hint once it has been implemented and used in the >>>>>> wild long enough. The kernel userspace regression rules make sure of >>>>>> that. >>>>> >>>>> Yeah, tricky and maybe a gray area in this case. I think we eluded >>>>> elsewhere in the thread that renaming the thing might be an option. >>>>> >>>>> So maybe instead of deadline, which is a very strong word, use something >>>>> along the lines of "present time hint", or "signalled time hint"? Maybe >>>>> reads clumsy. Just throwing some ideas for a start. >>>> >>>> You can try, but I fear that if it ever changes behaviour and >>>> someone notices that, it's labelled as a kernel regression. I don't >>>> think documentation has ever been the authoritative definition of UABI >>>> in Linux, it just guides drivers and userspace towards a common >>>> understanding and common usage patterns. >>>> >>>> So even if the UABI contract is not documented (ugh), you need to be >>>> prepared to set the UABI contract through kernel implementation. >>> >>> To be the devil's advocate it probably wouldn't be an ABI regression but >>> just an regression. Same way as what nice(2) priorities mean hasn't >>> always been the same over the years, I don't think there is a strict >>> contract. >>> >>> Having said that, it may be different with latency sensitive stuff such >>> as UIs though since it is very observable and can be very painful to users. >>> >>>> If you do not document the UABI contract, then different drivers are >>>> likely to implement it differently, leading to differing behaviour. >>>> Also userspace will invent wild ways to abuse the UABI if there is no >>>> documentation guiding it on proper use. If userspace or end users >>>> observe different behaviour, that's bad even if it's not a regression. >>>> >>>> I don't like the situation either, but it is what it is. UABI stability >>>> trumps everything regardless of whether it was documented or not. >>>> >>>> I bet userspace is going to use this as a "make it faster, make it >>>> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD >>>> library that stamps any and all fences with an expired deadline to >>>> just squeeze out a little more through some weird side-effect. >>>> >>>> Well, that's hopefully overboard in scaring, but in the end, I would >>>> like to see UABI documented so I can have a feeling of what it is for >>>> and how it was intended to be used. That's all. >>> >>> We share the same concern. If you read elsewhere in these threads you >>> will notice I have been calling this an "arms race". If the ability to >>> make yourself go faster does not required additional privilege I also >>> worry everyone will do it at which point it becomes pointless. So yes, I >>> do share this concern about exposing any of this as an unprivileged uapi. >>> >>> Is it possible to limit access to only compositors in some sane way? >>> Sounds tricky when dma-fence should be disconnected from DRM.. >> >> Maybe it's not that bad in this particular case, because we are talking >> only about boosting GPU clocks which benefits everyone (except >> battery life) and it does not penalize other programs like e.g. >> job priorities do. > > Apart from efficiency that you mentioned, which does not always favor > higher clocks, sometimes thermal budget is also shared between CPU and > GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to > make optimal choices without the full coordination between both schedulers. > > But that is even not the main point, which is that if everyone sets the > immediate deadline then having the deadline API is a bit pointless. For > instance there is a reason negative nice needs CAP_SYS_ADMIN. > > However Rob has also pointed out the existence of uclamp.min via > sched_setattr which is unprivileged and can influence frequency > selection in the CPU world, so I conceded on that point. If CPU world > has accepted it so can we I guess. > > So IMO we are back to whether we can agree defining it is a hint is good > enough, be in via the name of the ioctl/flag itself or via documentation. > >> Drivers are not going to use the deadline for scheduling priorities, >> right? I don't recall seeing any mention of that. >> >> ...right? > > I wouldn't have thought it would be beneficial to preclude that, or > assume what drivers would do with the info to begin with. > > For instance in i915 we almost had a deadline based scheduler which was > much fairer than the current priority sorted fifo and in an ideal world > we would either revive or re-implement that idea. In which case > considering the fence deadline would naturally slot in and give true > integration with compositor deadlines (not just boost clocks and pray it > helps). How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
the dynamic double/triple buffer thing?
Yes
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority.
This sounds like something orthogonal.. something for cgroups? Ie. android moves visible/foreground apps to a different cgroup to given them higher priority. Tvrtko had a patchset to add drm cgroup support..
For the priority stuff, yes, probably. The visibility information on the other hand could be used to determine if we want to ramp up the GPU in the first place.
We know when there are input events which actually matter.
This I see input as a different boost source for the driver. (Ie. one boost signal is missing fence deadlines, another is input events, etc.)
We end up using downstream input-handlers on the kernel side for this. Partially for the freq boost (but mostly not, UI interactive workloads like touchscreen scrolling don't generally need high GPU freqs, they are more memory bandwidth limited if they are limited by anything).. really the reason here is to get a head-start on the ~2ms that it takes to power up the GPU if it is suspended.
Right, but one of my main points I want to make here is that we could get the head-start not only in response to input events but also for the GPU work the compositor submits and in the future also to GPU work that clients commit. Except that we don't have a way to tell the kernel about it.
But this is not quite perfect, since for example some keys should be handled on key-down but others on key-up.
But again, this is something different from fence deadlines. I'm interested in proposals because we do need something for this. But I think it is something is orthogonal to this series. For input, we want the kernel to know long before userspace is ready to submit rendering.
We can do that in the compositor! Input events are really not something you should care about in the kernel. Input itself is also not the only indication of incoming animated content. Some network packets arriving could equally well result in the same situation.
We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
- The compositor has no way to communicate any of that information to
the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
If the client isn't using multiple GPUs, a single fence should be sufficient. And even if it is, well we still have all the dependency information on the kernel side. Ie. drm/sched knows what fences it is waiting on if it is waiting to schedule the work associated with the last fence. It would otherwise require drm/sched to be a bit more tricky than it is so far in this series.
But I think the normal dual-gpu case, the app is only dealing with a single GPU?
We generally don't know which GPU a client uses though. We know which one we're using and tell the client that the buffer should be compatible with it but that's the extent of information we have, until we get a fence but that fence usually gets to the compositor pretty late. Way too late for the compositor to tell the kernel to ramp up the GPU and still have an impact.
It also seems like we're moving away from tracking execution dependencies with fences when we're switching to user mode fences.
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
Yeah, I think the thing is you need multiple things, and this is only one of them ;-)
BR, -R
On Tue, Feb 28, 2023 at 6:30 AM Sebastian Wick sebastian.wick@redhat.com wrote:
On Tue, Feb 28, 2023 at 12:48 AM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 2:44 PM Sebastian Wick sebastian.wick@redhat.com wrote:
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote: > > On 2023-02-24 06:37, Tvrtko Ursulin wrote: > > > > On 24/02/2023 11:00, Pekka Paalanen wrote: > >> On Fri, 24 Feb 2023 10:50:51 +0000 > >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > >> > >>> On 24/02/2023 10:24, Pekka Paalanen wrote: > >>>> On Fri, 24 Feb 2023 09:41:46 +0000 > >>>> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > >>>> > >>>>> On 24/02/2023 09:26, Pekka Paalanen wrote: > >>>>>> On Thu, 23 Feb 2023 10:51:48 -0800 > >>>>>> Rob Clark robdclark@gmail.com wrote: > >>>>>> > >>>>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: > >>>>>>>> > >>>>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 > >>>>>>>> Rob Clark robdclark@gmail.com wrote: > >>>>>>>> > >>>>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: > >>>>>> > >>>>>> ... > >>>>>> > >>>>>>>>>> On another matter, if the application uses SET_DEADLINE with one > >>>>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with > >>>>>>>>>> another timestamp, what should happen? > >>>>>>>>> > >>>>>>>>> The expectation is that many deadline hints can be set on a fence. > >>>>>>>>> The fence signaller should track the soonest deadline. > >>>>>>>> > >>>>>>>> You need to document that as UAPI, since it is observable to userspace. > >>>>>>>> It would be bad if drivers or subsystems would differ in behaviour. > >>>>>>>> > >>>>>>> > >>>>>>> It is in the end a hint. It is about giving the driver more > >>>>>>> information so that it can make better choices. But the driver is > >>>>>>> even free to ignore it. So maybe "expectation" is too strong of a > >>>>>>> word. Rather, any other behavior doesn't really make sense. But it > >>>>>>> could end up being dictated by how the hw and/or fw works. > >>>>>> > >>>>>> It will stop being a hint once it has been implemented and used in the > >>>>>> wild long enough. The kernel userspace regression rules make sure of > >>>>>> that. > >>>>> > >>>>> Yeah, tricky and maybe a gray area in this case. I think we eluded > >>>>> elsewhere in the thread that renaming the thing might be an option. > >>>>> > >>>>> So maybe instead of deadline, which is a very strong word, use something > >>>>> along the lines of "present time hint", or "signalled time hint"? Maybe > >>>>> reads clumsy. Just throwing some ideas for a start. > >>>> > >>>> You can try, but I fear that if it ever changes behaviour and > >>>> someone notices that, it's labelled as a kernel regression. I don't > >>>> think documentation has ever been the authoritative definition of UABI > >>>> in Linux, it just guides drivers and userspace towards a common > >>>> understanding and common usage patterns. > >>>> > >>>> So even if the UABI contract is not documented (ugh), you need to be > >>>> prepared to set the UABI contract through kernel implementation. > >>> > >>> To be the devil's advocate it probably wouldn't be an ABI regression but > >>> just an regression. Same way as what nice(2) priorities mean hasn't > >>> always been the same over the years, I don't think there is a strict > >>> contract. > >>> > >>> Having said that, it may be different with latency sensitive stuff such > >>> as UIs though since it is very observable and can be very painful to users. > >>> > >>>> If you do not document the UABI contract, then different drivers are > >>>> likely to implement it differently, leading to differing behaviour. > >>>> Also userspace will invent wild ways to abuse the UABI if there is no > >>>> documentation guiding it on proper use. If userspace or end users > >>>> observe different behaviour, that's bad even if it's not a regression. > >>>> > >>>> I don't like the situation either, but it is what it is. UABI stability > >>>> trumps everything regardless of whether it was documented or not. > >>>> > >>>> I bet userspace is going to use this as a "make it faster, make it > >>>> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD > >>>> library that stamps any and all fences with an expired deadline to > >>>> just squeeze out a little more through some weird side-effect. > >>>> > >>>> Well, that's hopefully overboard in scaring, but in the end, I would > >>>> like to see UABI documented so I can have a feeling of what it is for > >>>> and how it was intended to be used. That's all. > >>> > >>> We share the same concern. If you read elsewhere in these threads you > >>> will notice I have been calling this an "arms race". If the ability to > >>> make yourself go faster does not required additional privilege I also > >>> worry everyone will do it at which point it becomes pointless. So yes, I > >>> do share this concern about exposing any of this as an unprivileged uapi. > >>> > >>> Is it possible to limit access to only compositors in some sane way? > >>> Sounds tricky when dma-fence should be disconnected from DRM.. > >> > >> Maybe it's not that bad in this particular case, because we are talking > >> only about boosting GPU clocks which benefits everyone (except > >> battery life) and it does not penalize other programs like e.g. > >> job priorities do. > > > > Apart from efficiency that you mentioned, which does not always favor > > higher clocks, sometimes thermal budget is also shared between CPU and > > GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to > > make optimal choices without the full coordination between both schedulers. > > > > But that is even not the main point, which is that if everyone sets the > > immediate deadline then having the deadline API is a bit pointless. For > > instance there is a reason negative nice needs CAP_SYS_ADMIN. > > > > However Rob has also pointed out the existence of uclamp.min via > > sched_setattr which is unprivileged and can influence frequency > > selection in the CPU world, so I conceded on that point. If CPU world > > has accepted it so can we I guess. > > > > So IMO we are back to whether we can agree defining it is a hint is good > > enough, be in via the name of the ioctl/flag itself or via documentation. > > > >> Drivers are not going to use the deadline for scheduling priorities, > >> right? I don't recall seeing any mention of that. > >> > >> ...right? > > > > I wouldn't have thought it would be beneficial to preclude that, or > > assume what drivers would do with the info to begin with. > > > > For instance in i915 we almost had a deadline based scheduler which was > > much fairer than the current priority sorted fifo and in an ideal world > > we would either revive or re-implement that idea. In which case > > considering the fence deadline would naturally slot in and give true > > integration with compositor deadlines (not just boost clocks and pray it > > helps). > How is user-space to decide whether to use ioctl(SET_DEADLINE) or > poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
the dynamic double/triple buffer thing?
Yes
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority.
This sounds like something orthogonal.. something for cgroups? Ie. android moves visible/foreground apps to a different cgroup to given them higher priority. Tvrtko had a patchset to add drm cgroup support..
For the priority stuff, yes, probably. The visibility information on the other hand could be used to determine if we want to ramp up the GPU in the first place.
Right, but I think that we could have multiple cgroup based knobs, one that adjusts priority and one that limits/disables deadline based boost? This way the compositor could setup different policies for visible vs hidden apps influencing both how much time they get on the GPU and boost.
We know when there are input events which actually matter.
This I see input as a different boost source for the driver. (Ie. one boost signal is missing fence deadlines, another is input events, etc.)
We end up using downstream input-handlers on the kernel side for this. Partially for the freq boost (but mostly not, UI interactive workloads like touchscreen scrolling don't generally need high GPU freqs, they are more memory bandwidth limited if they are limited by anything).. really the reason here is to get a head-start on the ~2ms that it takes to power up the GPU if it is suspended.
Right, but one of my main points I want to make here is that we could get the head-start not only in response to input events but also for the GPU work the compositor submits and in the future also to GPU work that clients commit. Except that we don't have a way to tell the kernel about it.
But this is not quite perfect, since for example some keys should be handled on key-down but others on key-up.
But again, this is something different from fence deadlines. I'm interested in proposals because we do need something for this. But I think it is something is orthogonal to this series. For input, we want the kernel to know long before userspace is ready to submit rendering.
We can do that in the compositor! Input events are really not something you should care about in the kernel. Input itself is also not the only indication of incoming animated content. Some network packets arriving could equally well result in the same situation.
We do use input boost not just for GPU freq, but also for CPU freq. It seems like triggering it from the kernel could happen somewhat sooner than userspace. (But just speculation.)
I'm not sure network packets count. Or at least compared to a touch interface, the user won't perceive the lag nearly as much, compared to whether or not the UI tracks their fingertips.
We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
- The compositor has no way to communicate any of that information to
the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
If the client isn't using multiple GPUs, a single fence should be sufficient. And even if it is, well we still have all the dependency information on the kernel side. Ie. drm/sched knows what fences it is waiting on if it is waiting to schedule the work associated with the last fence. It would otherwise require drm/sched to be a bit more tricky than it is so far in this series.
But I think the normal dual-gpu case, the app is only dealing with a single GPU?
We generally don't know which GPU a client uses though. We know which one we're using and tell the client that the buffer should be compatible with it but that's the extent of information we have, until we get a fence but that fence usually gets to the compositor pretty late. Way too late for the compositor to tell the kernel to ramp up the GPU and still have an impact.
Are you sure about that? I'd have expected the app to hand off fence+buffer to the compositor pretty quickly after rendering is submitted. This is what I've seen elsewhere.
It also seems like we're moving away from tracking execution dependencies with fences when we're switching to user mode fences.
I suppose there are two cases..
1) dependent fences all from the same device.. no prob, the right driver gets the signal that it needs to clk up, and figures out the rest on it's own
2) dependent fences from different devices.. I suppose if device B is waiting for a fence from device A before it can make forward progress, why not express this as a deadline hint on A's fence? (But by the time you have this problem, you are probably not really caring about power consumption, so meh..)
BR, -R
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
Yeah, I think the thing is you need multiple things, and this is only one of them ;-)
BR, -R
On Tue, Feb 28, 2023 at 11:52 PM Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 28, 2023 at 6:30 AM Sebastian Wick sebastian.wick@redhat.com wrote:
On Tue, Feb 28, 2023 at 12:48 AM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 2:44 PM Sebastian Wick sebastian.wick@redhat.com wrote:
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote: > On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote: > > > > On 2023-02-24 06:37, Tvrtko Ursulin wrote: > > > > > > On 24/02/2023 11:00, Pekka Paalanen wrote: > > >> On Fri, 24 Feb 2023 10:50:51 +0000 > > >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > > >> > > >>> On 24/02/2023 10:24, Pekka Paalanen wrote: > > >>>> On Fri, 24 Feb 2023 09:41:46 +0000 > > >>>> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > > >>>> > > >>>>> On 24/02/2023 09:26, Pekka Paalanen wrote: > > >>>>>> On Thu, 23 Feb 2023 10:51:48 -0800 > > >>>>>> Rob Clark robdclark@gmail.com wrote: > > >>>>>> > > >>>>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > >>>>>>>> > > >>>>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 > > >>>>>>>> Rob Clark robdclark@gmail.com wrote: > > >>>>>>>> > > >>>>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > >>>>>> > > >>>>>> ... > > >>>>>> > > >>>>>>>>>> On another matter, if the application uses SET_DEADLINE with one > > >>>>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with > > >>>>>>>>>> another timestamp, what should happen? > > >>>>>>>>> > > >>>>>>>>> The expectation is that many deadline hints can be set on a fence. > > >>>>>>>>> The fence signaller should track the soonest deadline. > > >>>>>>>> > > >>>>>>>> You need to document that as UAPI, since it is observable to userspace. > > >>>>>>>> It would be bad if drivers or subsystems would differ in behaviour. > > >>>>>>>> > > >>>>>>> > > >>>>>>> It is in the end a hint. It is about giving the driver more > > >>>>>>> information so that it can make better choices. But the driver is > > >>>>>>> even free to ignore it. So maybe "expectation" is too strong of a > > >>>>>>> word. Rather, any other behavior doesn't really make sense. But it > > >>>>>>> could end up being dictated by how the hw and/or fw works. > > >>>>>> > > >>>>>> It will stop being a hint once it has been implemented and used in the > > >>>>>> wild long enough. The kernel userspace regression rules make sure of > > >>>>>> that. > > >>>>> > > >>>>> Yeah, tricky and maybe a gray area in this case. I think we eluded > > >>>>> elsewhere in the thread that renaming the thing might be an option. > > >>>>> > > >>>>> So maybe instead of deadline, which is a very strong word, use something > > >>>>> along the lines of "present time hint", or "signalled time hint"? Maybe > > >>>>> reads clumsy. Just throwing some ideas for a start. > > >>>> > > >>>> You can try, but I fear that if it ever changes behaviour and > > >>>> someone notices that, it's labelled as a kernel regression. I don't > > >>>> think documentation has ever been the authoritative definition of UABI > > >>>> in Linux, it just guides drivers and userspace towards a common > > >>>> understanding and common usage patterns. > > >>>> > > >>>> So even if the UABI contract is not documented (ugh), you need to be > > >>>> prepared to set the UABI contract through kernel implementation. > > >>> > > >>> To be the devil's advocate it probably wouldn't be an ABI regression but > > >>> just an regression. Same way as what nice(2) priorities mean hasn't > > >>> always been the same over the years, I don't think there is a strict > > >>> contract. > > >>> > > >>> Having said that, it may be different with latency sensitive stuff such > > >>> as UIs though since it is very observable and can be very painful to users. > > >>> > > >>>> If you do not document the UABI contract, then different drivers are > > >>>> likely to implement it differently, leading to differing behaviour. > > >>>> Also userspace will invent wild ways to abuse the UABI if there is no > > >>>> documentation guiding it on proper use. If userspace or end users > > >>>> observe different behaviour, that's bad even if it's not a regression. > > >>>> > > >>>> I don't like the situation either, but it is what it is. UABI stability > > >>>> trumps everything regardless of whether it was documented or not. > > >>>> > > >>>> I bet userspace is going to use this as a "make it faster, make it > > >>>> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD > > >>>> library that stamps any and all fences with an expired deadline to > > >>>> just squeeze out a little more through some weird side-effect. > > >>>> > > >>>> Well, that's hopefully overboard in scaring, but in the end, I would > > >>>> like to see UABI documented so I can have a feeling of what it is for > > >>>> and how it was intended to be used. That's all. > > >>> > > >>> We share the same concern. If you read elsewhere in these threads you > > >>> will notice I have been calling this an "arms race". If the ability to > > >>> make yourself go faster does not required additional privilege I also > > >>> worry everyone will do it at which point it becomes pointless. So yes, I > > >>> do share this concern about exposing any of this as an unprivileged uapi. > > >>> > > >>> Is it possible to limit access to only compositors in some sane way? > > >>> Sounds tricky when dma-fence should be disconnected from DRM.. > > >> > > >> Maybe it's not that bad in this particular case, because we are talking > > >> only about boosting GPU clocks which benefits everyone (except > > >> battery life) and it does not penalize other programs like e.g. > > >> job priorities do. > > > > > > Apart from efficiency that you mentioned, which does not always favor > > > higher clocks, sometimes thermal budget is also shared between CPU and > > > GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to > > > make optimal choices without the full coordination between both schedulers. > > > > > > But that is even not the main point, which is that if everyone sets the > > > immediate deadline then having the deadline API is a bit pointless. For > > > instance there is a reason negative nice needs CAP_SYS_ADMIN. > > > > > > However Rob has also pointed out the existence of uclamp.min via > > > sched_setattr which is unprivileged and can influence frequency > > > selection in the CPU world, so I conceded on that point. If CPU world > > > has accepted it so can we I guess. > > > > > > So IMO we are back to whether we can agree defining it is a hint is good > > > enough, be in via the name of the ioctl/flag itself or via documentation. > > > > > >> Drivers are not going to use the deadline for scheduling priorities, > > >> right? I don't recall seeing any mention of that. > > >> > > >> ...right? > > > > > > I wouldn't have thought it would be beneficial to preclude that, or > > > assume what drivers would do with the info to begin with. > > > > > > For instance in i915 we almost had a deadline based scheduler which was > > > much fairer than the current priority sorted fifo and in an ideal world > > > we would either revive or re-implement that idea. In which case > > > considering the fence deadline would naturally slot in and give true > > > integration with compositor deadlines (not just boost clocks and pray it > > > helps). > > How is user-space to decide whether to use ioctl(SET_DEADLINE) or > > poll(POLLPRI)? > > Implementation of blocking gl/vk/cl APIs, like glFinish() would use > poll(POLLPRI). It could also set an immediate deadline and then call > poll() without POLLPRI. > > Other than compositors which do frame-pacing I expect the main usage > of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
the dynamic double/triple buffer thing?
Yes
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority.
This sounds like something orthogonal.. something for cgroups? Ie. android moves visible/foreground apps to a different cgroup to given them higher priority. Tvrtko had a patchset to add drm cgroup support..
For the priority stuff, yes, probably. The visibility information on the other hand could be used to determine if we want to ramp up the GPU in the first place.
Right, but I think that we could have multiple cgroup based knobs, one that adjusts priority and one that limits/disables deadline based boost? This way the compositor could setup different policies for visible vs hidden apps influencing both how much time they get on the GPU and boost.
I'm not sure if a negative control really makes sense. There are probably timing sensitive use cases where the result doesn't show up on the local screen and penalizing them when they are not focused or hidden might also not be the best idea.
We know when there are input events which actually matter.
This I see input as a different boost source for the driver. (Ie. one boost signal is missing fence deadlines, another is input events, etc.)
We end up using downstream input-handlers on the kernel side for this. Partially for the freq boost (but mostly not, UI interactive workloads like touchscreen scrolling don't generally need high GPU freqs, they are more memory bandwidth limited if they are limited by anything).. really the reason here is to get a head-start on the ~2ms that it takes to power up the GPU if it is suspended.
Right, but one of my main points I want to make here is that we could get the head-start not only in response to input events but also for the GPU work the compositor submits and in the future also to GPU work that clients commit. Except that we don't have a way to tell the kernel about it.
But this is not quite perfect, since for example some keys should be handled on key-down but others on key-up.
But again, this is something different from fence deadlines. I'm interested in proposals because we do need something for this. But I think it is something is orthogonal to this series. For input, we want the kernel to know long before userspace is ready to submit rendering.
We can do that in the compositor! Input events are really not something you should care about in the kernel. Input itself is also not the only indication of incoming animated content. Some network packets arriving could equally well result in the same situation.
We do use input boost not just for GPU freq, but also for CPU freq. It seems like triggering it from the kernel could happen somewhat sooner than userspace. (But just speculation.)
Technically it has to be sooner but I doubt it makes any difference. Getting a lot of false-positives on the other hand does make a difference.
I'm not sure network packets count. Or at least compared to a touch interface, the user won't perceive the lag nearly as much, compared to whether or not the UI tracks their fingertips.
Sure, stutter in interactive cases is especially awful but stutter is awful in general. If we can solve it in all cases we should do so.
We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
- The compositor has no way to communicate any of that information to
the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
If the client isn't using multiple GPUs, a single fence should be sufficient. And even if it is, well we still have all the dependency information on the kernel side. Ie. drm/sched knows what fences it is waiting on if it is waiting to schedule the work associated with the last fence. It would otherwise require drm/sched to be a bit more tricky than it is so far in this series.
But I think the normal dual-gpu case, the app is only dealing with a single GPU?
We generally don't know which GPU a client uses though. We know which one we're using and tell the client that the buffer should be compatible with it but that's the extent of information we have, until we get a fence but that fence usually gets to the compositor pretty late. Way too late for the compositor to tell the kernel to ramp up the GPU and still have an impact.
Are you sure about that? I'd have expected the app to hand off fence+buffer to the compositor pretty quickly after rendering is submitted. This is what I've seen elsewhere.
After rendering is submitted it is already too late if the GPU takes 2ms to wake up. And if there is no rendering submitted there is no fence and if there is no fence it has no deadline. If we want to solve that we also need some kind of 'work will be submitted to the queue starting from this time' hint.
It also seems like we're moving away from tracking execution dependencies with fences when we're switching to user mode fences.
I suppose there are two cases..
- dependent fences all from the same device.. no prob, the right
driver gets the signal that it needs to clk up, and figures out the rest on it's own
AFAIU with user mode fences it's impossible for the kernel to figure out what work depends on it and it might never signal. The whole deadline on fences thing breaks down with user mode fences.
- dependent fences from different devices.. I suppose if device B is
waiting for a fence from device A before it can make forward progress, why not express this as a deadline hint on A's fence? (But by the time you have this problem, you are probably not really caring about power consumption, so meh..)
BR, -R
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
Yeah, I think the thing is you need multiple things, and this is only one of them ;-)
BR, -R
On Wed, Mar 1, 2023 at 7:31 AM Sebastian Wick sebastian.wick@redhat.com wrote:
On Tue, Feb 28, 2023 at 11:52 PM Rob Clark robdclark@gmail.com wrote:
On Tue, Feb 28, 2023 at 6:30 AM Sebastian Wick sebastian.wick@redhat.com wrote:
On Tue, Feb 28, 2023 at 12:48 AM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 2:44 PM Sebastian Wick sebastian.wick@redhat.com wrote:
On Mon, Feb 27, 2023 at 11:20 PM Rob Clark robdclark@gmail.com wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote: > > On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote: > > On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote: > > > > > > On 2023-02-24 06:37, Tvrtko Ursulin wrote: > > > > > > > > On 24/02/2023 11:00, Pekka Paalanen wrote: > > > >> On Fri, 24 Feb 2023 10:50:51 +0000 > > > >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > > > >> > > > >>> On 24/02/2023 10:24, Pekka Paalanen wrote: > > > >>>> On Fri, 24 Feb 2023 09:41:46 +0000 > > > >>>> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: > > > >>>> > > > >>>>> On 24/02/2023 09:26, Pekka Paalanen wrote: > > > >>>>>> On Thu, 23 Feb 2023 10:51:48 -0800 > > > >>>>>> Rob Clark robdclark@gmail.com wrote: > > > >>>>>> > > > >>>>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > > >>>>>>>> > > > >>>>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 > > > >>>>>>>> Rob Clark robdclark@gmail.com wrote: > > > >>>>>>>> > > > >>>>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > > >>>>>> > > > >>>>>> ... > > > >>>>>> > > > >>>>>>>>>> On another matter, if the application uses SET_DEADLINE with one > > > >>>>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with > > > >>>>>>>>>> another timestamp, what should happen? > > > >>>>>>>>> > > > >>>>>>>>> The expectation is that many deadline hints can be set on a fence. > > > >>>>>>>>> The fence signaller should track the soonest deadline. > > > >>>>>>>> > > > >>>>>>>> You need to document that as UAPI, since it is observable to userspace. > > > >>>>>>>> It would be bad if drivers or subsystems would differ in behaviour. > > > >>>>>>>> > > > >>>>>>> > > > >>>>>>> It is in the end a hint. It is about giving the driver more > > > >>>>>>> information so that it can make better choices. But the driver is > > > >>>>>>> even free to ignore it. So maybe "expectation" is too strong of a > > > >>>>>>> word. Rather, any other behavior doesn't really make sense. But it > > > >>>>>>> could end up being dictated by how the hw and/or fw works. > > > >>>>>> > > > >>>>>> It will stop being a hint once it has been implemented and used in the > > > >>>>>> wild long enough. The kernel userspace regression rules make sure of > > > >>>>>> that. > > > >>>>> > > > >>>>> Yeah, tricky and maybe a gray area in this case. I think we eluded > > > >>>>> elsewhere in the thread that renaming the thing might be an option. > > > >>>>> > > > >>>>> So maybe instead of deadline, which is a very strong word, use something > > > >>>>> along the lines of "present time hint", or "signalled time hint"? Maybe > > > >>>>> reads clumsy. Just throwing some ideas for a start. > > > >>>> > > > >>>> You can try, but I fear that if it ever changes behaviour and > > > >>>> someone notices that, it's labelled as a kernel regression. I don't > > > >>>> think documentation has ever been the authoritative definition of UABI > > > >>>> in Linux, it just guides drivers and userspace towards a common > > > >>>> understanding and common usage patterns. > > > >>>> > > > >>>> So even if the UABI contract is not documented (ugh), you need to be > > > >>>> prepared to set the UABI contract through kernel implementation. > > > >>> > > > >>> To be the devil's advocate it probably wouldn't be an ABI regression but > > > >>> just an regression. Same way as what nice(2) priorities mean hasn't > > > >>> always been the same over the years, I don't think there is a strict > > > >>> contract. > > > >>> > > > >>> Having said that, it may be different with latency sensitive stuff such > > > >>> as UIs though since it is very observable and can be very painful to users. > > > >>> > > > >>>> If you do not document the UABI contract, then different drivers are > > > >>>> likely to implement it differently, leading to differing behaviour. > > > >>>> Also userspace will invent wild ways to abuse the UABI if there is no > > > >>>> documentation guiding it on proper use. If userspace or end users > > > >>>> observe different behaviour, that's bad even if it's not a regression. > > > >>>> > > > >>>> I don't like the situation either, but it is what it is. UABI stability > > > >>>> trumps everything regardless of whether it was documented or not. > > > >>>> > > > >>>> I bet userspace is going to use this as a "make it faster, make it > > > >>>> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD > > > >>>> library that stamps any and all fences with an expired deadline to > > > >>>> just squeeze out a little more through some weird side-effect. > > > >>>> > > > >>>> Well, that's hopefully overboard in scaring, but in the end, I would > > > >>>> like to see UABI documented so I can have a feeling of what it is for > > > >>>> and how it was intended to be used. That's all. > > > >>> > > > >>> We share the same concern. If you read elsewhere in these threads you > > > >>> will notice I have been calling this an "arms race". If the ability to > > > >>> make yourself go faster does not required additional privilege I also > > > >>> worry everyone will do it at which point it becomes pointless. So yes, I > > > >>> do share this concern about exposing any of this as an unprivileged uapi. > > > >>> > > > >>> Is it possible to limit access to only compositors in some sane way? > > > >>> Sounds tricky when dma-fence should be disconnected from DRM.. > > > >> > > > >> Maybe it's not that bad in this particular case, because we are talking > > > >> only about boosting GPU clocks which benefits everyone (except > > > >> battery life) and it does not penalize other programs like e.g. > > > >> job priorities do. > > > > > > > > Apart from efficiency that you mentioned, which does not always favor > > > > higher clocks, sometimes thermal budget is also shared between CPU and > > > > GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to > > > > make optimal choices without the full coordination between both schedulers. > > > > > > > > But that is even not the main point, which is that if everyone sets the > > > > immediate deadline then having the deadline API is a bit pointless. For > > > > instance there is a reason negative nice needs CAP_SYS_ADMIN. > > > > > > > > However Rob has also pointed out the existence of uclamp.min via > > > > sched_setattr which is unprivileged and can influence frequency > > > > selection in the CPU world, so I conceded on that point. If CPU world > > > > has accepted it so can we I guess. > > > > > > > > So IMO we are back to whether we can agree defining it is a hint is good > > > > enough, be in via the name of the ioctl/flag itself or via documentation. > > > > > > > >> Drivers are not going to use the deadline for scheduling priorities, > > > >> right? I don't recall seeing any mention of that. > > > >> > > > >> ...right? > > > > > > > > I wouldn't have thought it would be beneficial to preclude that, or > > > > assume what drivers would do with the info to begin with. > > > > > > > > For instance in i915 we almost had a deadline based scheduler which was > > > > much fairer than the current priority sorted fifo and in an ideal world > > > > we would either revive or re-implement that idea. In which case > > > > considering the fence deadline would naturally slot in and give true > > > > integration with compositor deadlines (not just boost clocks and pray it > > > > helps). > > > How is user-space to decide whether to use ioctl(SET_DEADLINE) or > > > poll(POLLPRI)? > > > > Implementation of blocking gl/vk/cl APIs, like glFinish() would use > > poll(POLLPRI). It could also set an immediate deadline and then call > > poll() without POLLPRI. > > > > Other than compositors which do frame-pacing I expect the main usage > > of either of these is mesa. > > Okay, so it looks like we already agreed that having a way to bump frequency > from userspace is acceptable. either because there are already other ways > that you can waste power and because this already acceptable in the CPU > world. > > But why we are doing this in hidden ways then? > > Why can't we have this hint per context that is getting executed? > (either with a boost-context flag or with some low/med/max or '-1' to '1' > value like the latency priority)? > > I don't like the waitboost because this heurisitic fails in some media cases. > I don't like the global setting because we might be alternating a top-priority > with low-priority cases... > > So, why not something per context in execution? >
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
First of all, I believe that the fence deadline hint is a good idea. With that being said, I also don't think it is sufficient in a lot of cases.
The one thing I was alluding to before and that Pekka mentioned as well is that mutter for example has a problem where we're missing the deadline consistently because the clocks don't ramp up fast enough and there is a MR which is just trying to keep the GPU busy to avoid this.
the dynamic double/triple buffer thing?
Yes
It would be much better if the kernel could make sure the clocks are all ramped up when we start submitting work. In the compositor we actually have a lot of information that *should* influence clocks. We know when we're going to start submitting work and when the deadline for that work is beforehand. We know which windows are visible, and which one should have the highest priority.
This sounds like something orthogonal.. something for cgroups? Ie. android moves visible/foreground apps to a different cgroup to given them higher priority. Tvrtko had a patchset to add drm cgroup support..
For the priority stuff, yes, probably. The visibility information on the other hand could be used to determine if we want to ramp up the GPU in the first place.
Right, but I think that we could have multiple cgroup based knobs, one that adjusts priority and one that limits/disables deadline based boost? This way the compositor could setup different policies for visible vs hidden apps influencing both how much time they get on the GPU and boost.
I'm not sure if a negative control really makes sense. There are probably timing sensitive use cases where the result doesn't show up on the local screen and penalizing them when they are not focused or hidden might also not be the best idea.
Policy decisions are up to the OS/distro.. we can only provide controls that can be tuned, it is up to someone else to choose how to use those controls, such as whether it wants to differentiate between visible and non-visible apps. That is why cgroups and a negative control are a good solution for controlling what the driver does with the deadline boost hint.
We know when there are input events which actually matter.
This I see input as a different boost source for the driver. (Ie. one boost signal is missing fence deadlines, another is input events, etc.)
We end up using downstream input-handlers on the kernel side for this. Partially for the freq boost (but mostly not, UI interactive workloads like touchscreen scrolling don't generally need high GPU freqs, they are more memory bandwidth limited if they are limited by anything).. really the reason here is to get a head-start on the ~2ms that it takes to power up the GPU if it is suspended.
Right, but one of my main points I want to make here is that we could get the head-start not only in response to input events but also for the GPU work the compositor submits and in the future also to GPU work that clients commit. Except that we don't have a way to tell the kernel about it.
But this is not quite perfect, since for example some keys should be handled on key-down but others on key-up.
But again, this is something different from fence deadlines. I'm interested in proposals because we do need something for this. But I think it is something is orthogonal to this series. For input, we want the kernel to know long before userspace is ready to submit rendering.
We can do that in the compositor! Input events are really not something you should care about in the kernel. Input itself is also not the only indication of incoming animated content. Some network packets arriving could equally well result in the same situation.
We do use input boost not just for GPU freq, but also for CPU freq. It seems like triggering it from the kernel could happen somewhat sooner than userspace. (But just speculation.)
Technically it has to be sooner but I doubt it makes any difference. Getting a lot of false-positives on the other hand does make a difference.
Regardless of whether it is done in kernel or userspace, you do want a cooldown period so you are not constantly boosting.
Generally false-positives aren't much of a problem.. ie. touch or mouse events are not ambiguous. The exception is key events, because ideally you don't want to hard-code in the kernel which keys are modifier keys that should be handled on key-up instead of key-down. But I think if we allowed userspace to configure this somehow, it would be perfectly reasonable (and optimal) to handle input boost in the kernel.
I'm not sure network packets count. Or at least compared to a touch interface, the user won't perceive the lag nearly as much, compared to whether or not the UI tracks their fingertips.
Sure, stutter in interactive cases is especially awful but stutter is awful in general. If we can solve it in all cases we should do so.
Sure, but the cases where I've seen a need for input boost are all about the transition from idle->active. Ie. the display panel has gone to self-refresh, gpu is suspended, cpu and memory is downclocked. And suddenly the user decides they want to start scrolling. We need some help to adapt to the new state where we are all of a sudden busy doing something. This is where input-boost comes in. If there is no direct connection to user input, then there is no lag for the user to percieve.
We know when the deadline for client work is.
In the future we also want to make sure clients know beforehand when they should start their work and when the deadline is but that's all very much WIP in both wayland and vulkan.
There are two issues:
- The compositor has no way to communicate any of that information to
the kernel. 2. The only connection to client work the compositor has is a fence to the last bit of work that must be done before the deadline after a wl_surface.commit.
If the client isn't using multiple GPUs, a single fence should be sufficient. And even if it is, well we still have all the dependency information on the kernel side. Ie. drm/sched knows what fences it is waiting on if it is waiting to schedule the work associated with the last fence. It would otherwise require drm/sched to be a bit more tricky than it is so far in this series.
But I think the normal dual-gpu case, the app is only dealing with a single GPU?
We generally don't know which GPU a client uses though. We know which one we're using and tell the client that the buffer should be compatible with it but that's the extent of information we have, until we get a fence but that fence usually gets to the compositor pretty late. Way too late for the compositor to tell the kernel to ramp up the GPU and still have an impact.
Are you sure about that? I'd have expected the app to hand off fence+buffer to the compositor pretty quickly after rendering is submitted. This is what I've seen elsewhere.
After rendering is submitted it is already too late if the GPU takes 2ms to wake up. And if there is no rendering submitted there is no fence and if there is no fence it has no deadline. If we want to solve that we also need some kind of 'work will be submitted to the queue starting from this time' hint.
Right, which is why I view this as a different problem with a different solution.
It also seems like we're moving away from tracking execution dependencies with fences when we're switching to user mode fences.
I suppose there are two cases..
- dependent fences all from the same device.. no prob, the right
driver gets the signal that it needs to clk up, and figures out the rest on it's own
AFAIU with user mode fences it's impossible for the kernel to figure out what work depends on it and it might never signal. The whole deadline on fences thing breaks down with user mode fences.
Given that user-mode fences are not a solved problem (and I don't think they'll ever completely replace kernel fences), I don't think this is relevant.
BR, -R
- dependent fences from different devices.. I suppose if device B is
waiting for a fence from device A before it can make forward progress, why not express this as a deadline hint on A's fence? (But by the time you have this problem, you are probably not really caring about power consumption, so meh..)
BR, -R
So in both cases a fence is just not the right primitive for us. We need to be able to provide per-context/queue information for work that will happen in the future and we need a way to refer to a context/queue generically and over IPC to boost the clocks of the device that a client is actually using and maybe even give priority.
But like I said, having a per-fence deadline is probably still a good idea and doesn't conflict with any of the more coarse information.
Yeah, I think the thing is you need multiple things, and this is only one of them ;-)
BR, -R
On Mon, Feb 27, 2023 at 02:20:04PM -0800, Rob Clark wrote:
On Mon, Feb 27, 2023 at 1:36 PM Rodrigo Vivi rodrigo.vivi@intel.com wrote:
On Fri, Feb 24, 2023 at 09:59:57AM -0800, Rob Clark wrote:
On Fri, Feb 24, 2023 at 7:27 AM Luben Tuikov luben.tuikov@amd.com wrote:
On 2023-02-24 06:37, Tvrtko Ursulin wrote:
On 24/02/2023 11:00, Pekka Paalanen wrote:
On Fri, 24 Feb 2023 10:50:51 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
> On 24/02/2023 10:24, Pekka Paalanen wrote: >> On Fri, 24 Feb 2023 09:41:46 +0000 >> Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote: >> >>> On 24/02/2023 09:26, Pekka Paalanen wrote: >>>> On Thu, 23 Feb 2023 10:51:48 -0800 >>>> Rob Clark robdclark@gmail.com wrote: >>>> >>>>> On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>>>> >>>>>> On Wed, 22 Feb 2023 07:37:26 -0800 >>>>>> Rob Clark robdclark@gmail.com wrote: >>>>>> >>>>>>> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote: >>>> >>>> ... >>>> >>>>>>>> On another matter, if the application uses SET_DEADLINE with one >>>>>>>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>>>>>>> another timestamp, what should happen? >>>>>>> >>>>>>> The expectation is that many deadline hints can be set on a fence. >>>>>>> The fence signaller should track the soonest deadline. >>>>>> >>>>>> You need to document that as UAPI, since it is observable to userspace. >>>>>> It would be bad if drivers or subsystems would differ in behaviour. >>>>>> >>>>> >>>>> It is in the end a hint. It is about giving the driver more >>>>> information so that it can make better choices. But the driver is >>>>> even free to ignore it. So maybe "expectation" is too strong of a >>>>> word. Rather, any other behavior doesn't really make sense. But it >>>>> could end up being dictated by how the hw and/or fw works. >>>> >>>> It will stop being a hint once it has been implemented and used in the >>>> wild long enough. The kernel userspace regression rules make sure of >>>> that. >>> >>> Yeah, tricky and maybe a gray area in this case. I think we eluded >>> elsewhere in the thread that renaming the thing might be an option. >>> >>> So maybe instead of deadline, which is a very strong word, use something >>> along the lines of "present time hint", or "signalled time hint"? Maybe >>> reads clumsy. Just throwing some ideas for a start. >> >> You can try, but I fear that if it ever changes behaviour and >> someone notices that, it's labelled as a kernel regression. I don't >> think documentation has ever been the authoritative definition of UABI >> in Linux, it just guides drivers and userspace towards a common >> understanding and common usage patterns. >> >> So even if the UABI contract is not documented (ugh), you need to be >> prepared to set the UABI contract through kernel implementation. > > To be the devil's advocate it probably wouldn't be an ABI regression but > just an regression. Same way as what nice(2) priorities mean hasn't > always been the same over the years, I don't think there is a strict > contract. > > Having said that, it may be different with latency sensitive stuff such > as UIs though since it is very observable and can be very painful to users. > >> If you do not document the UABI contract, then different drivers are >> likely to implement it differently, leading to differing behaviour. >> Also userspace will invent wild ways to abuse the UABI if there is no >> documentation guiding it on proper use. If userspace or end users >> observe different behaviour, that's bad even if it's not a regression. >> >> I don't like the situation either, but it is what it is. UABI stability >> trumps everything regardless of whether it was documented or not. >> >> I bet userspace is going to use this as a "make it faster, make it >> hotter" button. I would not be surprised if someone wrote a LD_PRELOAD >> library that stamps any and all fences with an expired deadline to >> just squeeze out a little more through some weird side-effect. >> >> Well, that's hopefully overboard in scaring, but in the end, I would >> like to see UABI documented so I can have a feeling of what it is for >> and how it was intended to be used. That's all. > > We share the same concern. If you read elsewhere in these threads you > will notice I have been calling this an "arms race". If the ability to > make yourself go faster does not required additional privilege I also > worry everyone will do it at which point it becomes pointless. So yes, I > do share this concern about exposing any of this as an unprivileged uapi. > > Is it possible to limit access to only compositors in some sane way? > Sounds tricky when dma-fence should be disconnected from DRM..
Maybe it's not that bad in this particular case, because we are talking only about boosting GPU clocks which benefits everyone (except battery life) and it does not penalize other programs like e.g. job priorities do.
Apart from efficiency that you mentioned, which does not always favor higher clocks, sometimes thermal budget is also shared between CPU and GPU. So more GPU clocks can mean fewer CPU clocks. It's really hard to make optimal choices without the full coordination between both schedulers.
But that is even not the main point, which is that if everyone sets the immediate deadline then having the deadline API is a bit pointless. For instance there is a reason negative nice needs CAP_SYS_ADMIN.
However Rob has also pointed out the existence of uclamp.min via sched_setattr which is unprivileged and can influence frequency selection in the CPU world, so I conceded on that point. If CPU world has accepted it so can we I guess.
So IMO we are back to whether we can agree defining it is a hint is good enough, be in via the name of the ioctl/flag itself or via documentation.
Drivers are not going to use the deadline for scheduling priorities, right? I don't recall seeing any mention of that.
...right?
I wouldn't have thought it would be beneficial to preclude that, or assume what drivers would do with the info to begin with.
For instance in i915 we almost had a deadline based scheduler which was much fairer than the current priority sorted fifo and in an ideal world we would either revive or re-implement that idea. In which case considering the fence deadline would naturally slot in and give true integration with compositor deadlines (not just boost clocks and pray it helps).
How is user-space to decide whether to use ioctl(SET_DEADLINE) or poll(POLLPRI)?
Implementation of blocking gl/vk/cl APIs, like glFinish() would use poll(POLLPRI). It could also set an immediate deadline and then call poll() without POLLPRI.
Other than compositors which do frame-pacing I expect the main usage of either of these is mesa.
Okay, so it looks like we already agreed that having a way to bump frequency from userspace is acceptable. either because there are already other ways that you can waste power and because this already acceptable in the CPU world.
But why we are doing this in hidden ways then?
Why can't we have this hint per context that is getting executed? (either with a boost-context flag or with some low/med/max or '-1' to '1' value like the latency priority)?
I don't like the waitboost because this heurisitic fails in some media cases. I don't like the global setting because we might be alternating a top-priority with low-priority cases...
So, why not something per context in execution?
It needs to be finer granularity than per-context, because not all waits should trigger boosting. For example, virglrenderer ends up with a thread polling unsignaled fences to know when to signal an interrupt to the guest virtgpu. This alone shouldn't trigger boosting. (We also wouldn't want to completely disable boosting for virglrenderer.) Or the usermode driver could be waiting on a fence to know when to do some cleanup.
That is not to say that there isn't room for per-context flags to disable/enable boosting for fences created by that context, meaning it could be an AND operation for i915 if it needs to be.
Right. It can be both ways I agree.
BR, -R
On Fri, Feb 24, 2023 at 2:24 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
> On another matter, if the application uses SET_DEADLINE with one > timestamp, and the compositor uses SET_DEADLINE on the same thing with > another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Ok, maybe we can rename the SET_DEADLINE ioctl to SPACEBAR_HEATER ;-)
BR, -R
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
Thanks, pq
On Fri, Feb 24, 2023 at 2:24 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote:
On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
> On another matter, if the application uses SET_DEADLINE with one > timestamp, and the compositor uses SET_DEADLINE on the same thing with > another timestamp, what should happen?
The expectation is that many deadline hints can be set on a fence. The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Userspace already has various (driver specific) debugfs/sysfs that it can use if it wants to make it hotter and drain batteries faster, so I'm not seeing a strong need to cater to the "turn it up to eleven" crowd here. And really your point feels like a good reason to _not_ document this as anything more than a hint.
Back in the real world, mobile games are already well aware of the fps vs battery-life (and therefore gameplay) tradeoff. But what is missing is a way to inform the kernel of userspace's intentions, so that gpu dvfs can make intelligent decisions. This series is meant to bridge that gap.
BR, -R
Well, that's hopefully overboard in scaring, but in the end, I would like to see UABI documented so I can have a feeling of what it is for and how it was intended to be used. That's all.
Thanks, pq
On Fri, 24 Feb 2023 11:44:53 -0800 Rob Clark robdclark@gmail.com wrote:
On Fri, Feb 24, 2023 at 2:24 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Wed, 22 Feb 2023 07:37:26 -0800 Rob Clark robdclark@gmail.com wrote: > On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
>> On another matter, if the application uses SET_DEADLINE with one >> timestamp, and the compositor uses SET_DEADLINE on the same thing with >> another timestamp, what should happen? > > The expectation is that many deadline hints can be set on a fence. > The fence signaller should track the soonest deadline.
You need to document that as UAPI, since it is observable to userspace. It would be bad if drivers or subsystems would differ in behaviour.
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Userspace already has various (driver specific) debugfs/sysfs that it can use if it wants to make it hotter and drain batteries faster, so I'm not seeing a strong need to cater to the "turn it up to eleven" crowd here. And really your point feels like a good reason to _not_ document this as anything more than a hint.
My point is that no matter what you say in documentation or leave unsaid, people can and will abuse this by the behaviour it provides anyway, like every other UABI.
So why not just document what it is supposed to do? It cannot get any worse. Maybe you get lucky instead and people don't abuse it that much if they read the docs.
E.g. can it affect GPU job scheduling, can it affect GPU clocks, can it affect power consumption, and so on.
Back in the real world, mobile games are already well aware of the fps vs battery-life (and therefore gameplay) tradeoff. But what is missing is a way to inform the kernel of userspace's intentions, so that gpu dvfs can make intelligent decisions. This series is meant to bridge that gap.
Then document that. As long as you document it properly: what you expect it to be used for and how.
Or if this is reserved strictly for Mesa drivers, then document that.
You can also stop CC'ing me if you don't want attention to UABI docs. I don't read dri-devel@ unless I'm explicitly CC'd nowadays.
Thanks, pq
On Mon, Feb 27, 2023 at 1:34 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Fri, 24 Feb 2023 11:44:53 -0800 Rob Clark robdclark@gmail.com wrote:
On Fri, Feb 24, 2023 at 2:24 AM Pekka Paalanen ppaalanen@gmail.com wrote:
On Fri, 24 Feb 2023 09:41:46 +0000 Tvrtko Ursulin tvrtko.ursulin@linux.intel.com wrote:
On 24/02/2023 09:26, Pekka Paalanen wrote:
On Thu, 23 Feb 2023 10:51:48 -0800 Rob Clark robdclark@gmail.com wrote:
On Thu, Feb 23, 2023 at 1:38 AM Pekka Paalanen ppaalanen@gmail.com wrote: > > On Wed, 22 Feb 2023 07:37:26 -0800 > Rob Clark robdclark@gmail.com wrote: > >> On Wed, Feb 22, 2023 at 1:49 AM Pekka Paalanen ppaalanen@gmail.com wrote:
...
>>> On another matter, if the application uses SET_DEADLINE with one >>> timestamp, and the compositor uses SET_DEADLINE on the same thing with >>> another timestamp, what should happen? >> >> The expectation is that many deadline hints can be set on a fence. >> The fence signaller should track the soonest deadline. > > You need to document that as UAPI, since it is observable to userspace. > It would be bad if drivers or subsystems would differ in behaviour. >
It is in the end a hint. It is about giving the driver more information so that it can make better choices. But the driver is even free to ignore it. So maybe "expectation" is too strong of a word. Rather, any other behavior doesn't really make sense. But it could end up being dictated by how the hw and/or fw works.
It will stop being a hint once it has been implemented and used in the wild long enough. The kernel userspace regression rules make sure of that.
Yeah, tricky and maybe a gray area in this case. I think we eluded elsewhere in the thread that renaming the thing might be an option.
So maybe instead of deadline, which is a very strong word, use something along the lines of "present time hint", or "signalled time hint"? Maybe reads clumsy. Just throwing some ideas for a start.
You can try, but I fear that if it ever changes behaviour and someone notices that, it's labelled as a kernel regression. I don't think documentation has ever been the authoritative definition of UABI in Linux, it just guides drivers and userspace towards a common understanding and common usage patterns.
So even if the UABI contract is not documented (ugh), you need to be prepared to set the UABI contract through kernel implementation.
If you do not document the UABI contract, then different drivers are likely to implement it differently, leading to differing behaviour. Also userspace will invent wild ways to abuse the UABI if there is no documentation guiding it on proper use. If userspace or end users observe different behaviour, that's bad even if it's not a regression.
I don't like the situation either, but it is what it is. UABI stability trumps everything regardless of whether it was documented or not.
I bet userspace is going to use this as a "make it faster, make it hotter" button. I would not be surprised if someone wrote a LD_PRELOAD library that stamps any and all fences with an expired deadline to just squeeze out a little more through some weird side-effect.
Userspace already has various (driver specific) debugfs/sysfs that it can use if it wants to make it hotter and drain batteries faster, so I'm not seeing a strong need to cater to the "turn it up to eleven" crowd here. And really your point feels like a good reason to _not_ document this as anything more than a hint.
My point is that no matter what you say in documentation or leave unsaid, people can and will abuse this by the behaviour it provides anyway, like every other UABI.
So why not just document what it is supposed to do? It cannot get any worse. Maybe you get lucky instead and people don't abuse it that much if they read the docs.
E.g. can it affect GPU job scheduling, can it affect GPU clocks, can it affect power consumption, and so on.
I expect, potentially, all or any, or none of the above ;-)
I guess I could document it as such, just to preempt potential complaints about broken spacebar-heater. The question is, where? I could add something about fence deadline hints in dma-buf.rst, which would I think be useful in general for driver writers. But there isn't really any existing documents other than headerdoc comments for sync_file ioctls, or drm_syncobj related ioctls (the latter are really just for mesa to use, so maybe that is ok).
Back in the real world, mobile games are already well aware of the fps vs battery-life (and therefore gameplay) tradeoff. But what is missing is a way to inform the kernel of userspace's intentions, so that gpu dvfs can make intelligent decisions. This series is meant to bridge that gap.
Then document that. As long as you document it properly: what you expect it to be used for and how.
Or if this is reserved strictly for Mesa drivers, then document that.
I expect the SET_DEADLINE ioctl to be useful to compositors, and maybe a few other cases. I'd like to use it in virglrenderer to bridge guest deadline hints to host kernel, for example.
BR, -R
You can also stop CC'ing me if you don't want attention to UABI docs. I don't read dri-devel@ unless I'm explicitly CC'd nowadays.
Thanks, pq
From: Rob Clark robdclark@chromium.org
This consists of simply storing the most recent deadline, and adding an ioctl to retrieve the deadline. This can be used in conjunction with the SET_DEADLINE ioctl on a fence fd for testing. Ie. create various sw_sync fences, merge them into a fence-array, set deadline on the fence-array and confirm that it is propagated properly to each fence.
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/dma-buf/sw_sync.c | 58 ++++++++++++++++++++++++++++++++++++ drivers/dma-buf/sync_debug.h | 2 ++ 2 files changed, 60 insertions(+)
diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index 348b3a9170fa..50f2638cccd3 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -52,12 +52,26 @@ struct sw_sync_create_fence_data { __s32 fence; /* fd of new fence */ };
+/** + * struct sw_sync_get_deadline - get the deadline of a sw_sync fence + * @tv_sec: seconds elapsed since epoch (out) + * @tv_nsec: nanoseconds elapsed since the time given by the tv_sec (out) + * @fence_fd: the sw_sync fence fd (in) + */ +struct sw_sync_get_deadline { + __s64 tv_sec; + __s32 tv_nsec; + __s32 fence_fd; +}; + #define SW_SYNC_IOC_MAGIC 'W'
#define SW_SYNC_IOC_CREATE_FENCE _IOWR(SW_SYNC_IOC_MAGIC, 0,\ struct sw_sync_create_fence_data)
#define SW_SYNC_IOC_INC _IOW(SW_SYNC_IOC_MAGIC, 1, __u32) +#define SW_SYNC_GET_DEADLINE _IOWR(SW_SYNC_IOC_MAGIC, 2, \ + struct sw_sync_get_deadline)
static const struct dma_fence_ops timeline_fence_ops;
@@ -171,6 +185,13 @@ static void timeline_fence_timeline_value_str(struct dma_fence *fence, snprintf(str, size, "%d", parent->value); }
+static void timeline_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + struct sync_pt *pt = dma_fence_to_sync_pt(fence); + + pt->deadline = deadline; +} + static const struct dma_fence_ops timeline_fence_ops = { .get_driver_name = timeline_fence_get_driver_name, .get_timeline_name = timeline_fence_get_timeline_name, @@ -179,6 +200,7 @@ static const struct dma_fence_ops timeline_fence_ops = { .release = timeline_fence_release, .fence_value_str = timeline_fence_value_str, .timeline_value_str = timeline_fence_timeline_value_str, + .set_deadline = timeline_fence_set_deadline, };
/** @@ -387,6 +409,39 @@ static long sw_sync_ioctl_inc(struct sync_timeline *obj, unsigned long arg) return 0; }
+static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long arg) +{ + struct sw_sync_get_deadline data; + struct timespec64 ts; + struct dma_fence *fence; + struct sync_pt *pt; + + if (copy_from_user(&data, (void __user *)arg, sizeof(data))) + return -EFAULT; + + if (data.tv_sec || data.tv_nsec) + return -EINVAL; + + fence = sync_file_get_fence(data.fence_fd); + if (!fence) + return -EINVAL; + + pt = dma_fence_to_sync_pt(fence); + if (!pt) + return -EINVAL; + + ts = ktime_to_timespec64(pt->deadline); + data.tv_sec = ts.tv_sec; + data.tv_nsec = ts.tv_nsec; + + dma_fence_put(fence); + + if (copy_to_user((void __user *)arg, &data, sizeof(data))) + return -EFAULT; + + return 0; +} + static long sw_sync_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -399,6 +454,9 @@ static long sw_sync_ioctl(struct file *file, unsigned int cmd, case SW_SYNC_IOC_INC: return sw_sync_ioctl_inc(obj, arg);
+ case SW_SYNC_GET_DEADLINE: + return sw_sync_ioctl_get_deadline(obj, arg); + default: return -ENOTTY; } diff --git a/drivers/dma-buf/sync_debug.h b/drivers/dma-buf/sync_debug.h index 6176e52ba2d7..2e0146d0bdbb 100644 --- a/drivers/dma-buf/sync_debug.h +++ b/drivers/dma-buf/sync_debug.h @@ -55,11 +55,13 @@ static inline struct sync_timeline *dma_fence_parent(struct dma_fence *fence) * @base: base fence object * @link: link on the sync timeline's list * @node: node in the sync timeline's tree + * @deadline: the most recently set fence deadline */ struct sync_pt { struct dma_fence base; struct list_head link; struct rb_node node; + ktime_t deadline; };
extern const struct file_operations sw_sync_debugfs_fops;
Am 18.02.23 um 22:15 schrieb Rob Clark:
From: Rob Clark robdclark@chromium.org
This consists of simply storing the most recent deadline, and adding an ioctl to retrieve the deadline. This can be used in conjunction with the SET_DEADLINE ioctl on a fence fd for testing. Ie. create various sw_sync fences, merge them into a fence-array, set deadline on the fence-array and confirm that it is propagated properly to each fence.
Signed-off-by: Rob Clark robdclark@chromium.org
Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/sw_sync.c | 58 ++++++++++++++++++++++++++++++++++++ drivers/dma-buf/sync_debug.h | 2 ++ 2 files changed, 60 insertions(+)
diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index 348b3a9170fa..50f2638cccd3 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -52,12 +52,26 @@ struct sw_sync_create_fence_data { __s32 fence; /* fd of new fence */ }; +/**
- struct sw_sync_get_deadline - get the deadline of a sw_sync fence
- @tv_sec: seconds elapsed since epoch (out)
- @tv_nsec: nanoseconds elapsed since the time given by the tv_sec (out)
- @fence_fd: the sw_sync fence fd (in)
- */
+struct sw_sync_get_deadline {
- __s64 tv_sec;
- __s32 tv_nsec;
- __s32 fence_fd;
+};
- #define SW_SYNC_IOC_MAGIC 'W'
#define SW_SYNC_IOC_CREATE_FENCE _IOWR(SW_SYNC_IOC_MAGIC, 0,\ struct sw_sync_create_fence_data) #define SW_SYNC_IOC_INC _IOW(SW_SYNC_IOC_MAGIC, 1, __u32) +#define SW_SYNC_GET_DEADLINE _IOWR(SW_SYNC_IOC_MAGIC, 2, \
struct sw_sync_get_deadline)static const struct dma_fence_ops timeline_fence_ops; @@ -171,6 +185,13 @@ static void timeline_fence_timeline_value_str(struct dma_fence *fence, snprintf(str, size, "%d", parent->value); } +static void timeline_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- struct sync_pt *pt = dma_fence_to_sync_pt(fence);
- pt->deadline = deadline;
+}
- static const struct dma_fence_ops timeline_fence_ops = { .get_driver_name = timeline_fence_get_driver_name, .get_timeline_name = timeline_fence_get_timeline_name,
@@ -179,6 +200,7 @@ static const struct dma_fence_ops timeline_fence_ops = { .release = timeline_fence_release, .fence_value_str = timeline_fence_value_str, .timeline_value_str = timeline_fence_timeline_value_str,
- .set_deadline = timeline_fence_set_deadline, };
/** @@ -387,6 +409,39 @@ static long sw_sync_ioctl_inc(struct sync_timeline *obj, unsigned long arg) return 0; } +static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long arg) +{
- struct sw_sync_get_deadline data;
- struct timespec64 ts;
- struct dma_fence *fence;
- struct sync_pt *pt;
- if (copy_from_user(&data, (void __user *)arg, sizeof(data)))
return -EFAULT;- if (data.tv_sec || data.tv_nsec)
return -EINVAL;- fence = sync_file_get_fence(data.fence_fd);
- if (!fence)
return -EINVAL;- pt = dma_fence_to_sync_pt(fence);
- if (!pt)
return -EINVAL;- ts = ktime_to_timespec64(pt->deadline);
- data.tv_sec = ts.tv_sec;
- data.tv_nsec = ts.tv_nsec;
- dma_fence_put(fence);
- if (copy_to_user((void __user *)arg, &data, sizeof(data)))
return -EFAULT;- return 0;
+}
- static long sw_sync_ioctl(struct file *file, unsigned int cmd, unsigned long arg) {
@@ -399,6 +454,9 @@ static long sw_sync_ioctl(struct file *file, unsigned int cmd, case SW_SYNC_IOC_INC: return sw_sync_ioctl_inc(obj, arg);
- case SW_SYNC_GET_DEADLINE:
return sw_sync_ioctl_get_deadline(obj, arg);- default: return -ENOTTY; }
diff --git a/drivers/dma-buf/sync_debug.h b/drivers/dma-buf/sync_debug.h index 6176e52ba2d7..2e0146d0bdbb 100644 --- a/drivers/dma-buf/sync_debug.h +++ b/drivers/dma-buf/sync_debug.h @@ -55,11 +55,13 @@ static inline struct sync_timeline *dma_fence_parent(struct dma_fence *fence)
- @base: base fence object
- @link: link on the sync timeline's list
- @node: node in the sync timeline's tree
*/ struct sync_pt { struct dma_fence base; struct list_head link; struct rb_node node;
- @deadline: the most recently set fence deadline
- ktime_t deadline; };
extern const struct file_operations sw_sync_debugfs_fops;
As the finished fence is the one that is exposed to userspace, and therefore the one that other operations, like atomic update, would block on, we need to propagate the deadline from from the finished fence to the actual hw fence.
v2: Split into drm_sched_fence_set_parent() (ckoenig) v3: Ensure a thread calling drm_sched_fence_set_deadline_finished() sees fence->parent set before drm_sched_fence_set_parent() does this test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT).
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/gpu/drm/scheduler/sched_fence.c | 46 +++++++++++++++++++++++++ drivers/gpu/drm/scheduler/sched_main.c | 2 +- include/drm/gpu_scheduler.h | 8 +++++ 3 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c index 7fd869520ef2..43e2d4f5fe3b 100644 --- a/drivers/gpu/drm/scheduler/sched_fence.c +++ b/drivers/gpu/drm/scheduler/sched_fence.c @@ -123,6 +123,37 @@ static void drm_sched_fence_release_finished(struct dma_fence *f) dma_fence_put(&fence->scheduled); }
+static void drm_sched_fence_set_deadline_finished(struct dma_fence *f, + ktime_t deadline) +{ + struct drm_sched_fence *fence = to_drm_sched_fence(f); + struct dma_fence *parent; + unsigned long flags; + + spin_lock_irqsave(&fence->lock, flags); + + /* If we already have an earlier deadline, keep it: */ + if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &f->flags) && + ktime_before(fence->deadline, deadline)) { + spin_unlock_irqrestore(&fence->lock, flags); + return; + } + + fence->deadline = deadline; + set_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &f->flags); + + spin_unlock_irqrestore(&fence->lock, flags); + + /* + * smp_load_aquire() to ensure that if we are racing another + * thread calling drm_sched_fence_set_parent(), that we see + * the parent set before it calls test_bit(HAS_DEADLINE_BIT) + */ + parent = smp_load_acquire(&fence->parent); + if (parent) + dma_fence_set_deadline(parent, deadline); +} + static const struct dma_fence_ops drm_sched_fence_ops_scheduled = { .get_driver_name = drm_sched_fence_get_driver_name, .get_timeline_name = drm_sched_fence_get_timeline_name, @@ -133,6 +164,7 @@ static const struct dma_fence_ops drm_sched_fence_ops_finished = { .get_driver_name = drm_sched_fence_get_driver_name, .get_timeline_name = drm_sched_fence_get_timeline_name, .release = drm_sched_fence_release_finished, + .set_deadline = drm_sched_fence_set_deadline_finished, };
struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f) @@ -147,6 +179,20 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f) } EXPORT_SYMBOL(to_drm_sched_fence);
+void drm_sched_fence_set_parent(struct drm_sched_fence *s_fence, + struct dma_fence *fence) +{ + /* + * smp_store_release() to ensure another thread racing us + * in drm_sched_fence_set_deadline_finished() sees the + * fence's parent set before test_bit() + */ + smp_store_release(&s_fence->parent, dma_fence_get(fence)); + if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, + &s_fence->finished.flags)) + dma_fence_set_deadline(fence, s_fence->deadline); +} + struct drm_sched_fence *drm_sched_fence_alloc(struct drm_sched_entity *entity, void *owner) { diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c index 4e6ad6e122bc..007f98c48f8d 100644 --- a/drivers/gpu/drm/scheduler/sched_main.c +++ b/drivers/gpu/drm/scheduler/sched_main.c @@ -1019,7 +1019,7 @@ static int drm_sched_main(void *param) drm_sched_fence_scheduled(s_fence);
if (!IS_ERR_OR_NULL(fence)) { - s_fence->parent = dma_fence_get(fence); + drm_sched_fence_set_parent(s_fence, fence); /* Drop for original kref_init of the fence */ dma_fence_put(fence);
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h index 9db9e5e504ee..8b31a954a44d 100644 --- a/include/drm/gpu_scheduler.h +++ b/include/drm/gpu_scheduler.h @@ -280,6 +280,12 @@ struct drm_sched_fence { */ struct dma_fence finished;
+ /** + * @deadline: deadline set on &drm_sched_fence.finished which + * potentially needs to be propagated to &drm_sched_fence.parent + */ + ktime_t deadline; + /** * @parent: the fence returned by &drm_sched_backend_ops.run_job * when scheduling the job on hardware. We signal the @@ -568,6 +574,8 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity, enum drm_sched_priority priority); bool drm_sched_entity_is_ready(struct drm_sched_entity *entity);
+void drm_sched_fence_set_parent(struct drm_sched_fence *s_fence, + struct dma_fence *fence); struct drm_sched_fence *drm_sched_fence_alloc( struct drm_sched_entity *s_entity, void *owner); void drm_sched_fence_init(struct drm_sched_fence *fence,
On 2023-02-18 16:15, Rob Clark wrote:
As the finished fence is the one that is exposed to userspace, and therefore the one that other operations, like atomic update, would block on, we need to propagate the deadline from from the finished fence to the actual hw fence.
v2: Split into drm_sched_fence_set_parent() (ckoenig) v3: Ensure a thread calling drm_sched_fence_set_deadline_finished() sees fence->parent set before drm_sched_fence_set_parent() does this test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT).
Signed-off-by: Rob Clark robdclark@chromium.org
Looks good.
This patch is Acked-by: Luben Tuikov luben.tuikov@amd.com
From: Rob Clark robdclark@chromium.org
Track the nearest deadline on a fence timeline and set a timer to expire shortly before to trigger boost if the fence has not yet been signaled.
Signed-off-by: Rob Clark robdclark@chromium.org --- drivers/gpu/drm/msm/msm_drv.c | 4 +- drivers/gpu/drm/msm/msm_fence.c | 74 +++++++++++++++++++++++++++++++++ drivers/gpu/drm/msm/msm_fence.h | 20 +++++++++ 3 files changed, 97 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c index aca48c868c14..be2a68f8e78d 100644 --- a/drivers/gpu/drm/msm/msm_drv.c +++ b/drivers/gpu/drm/msm/msm_drv.c @@ -1065,7 +1065,9 @@ static const struct drm_driver msm_driver = { DRIVER_RENDER | DRIVER_ATOMIC | DRIVER_MODESET | - DRIVER_SYNCOBJ, + DRIVER_SYNCOBJ | + DRIVER_SYNCOBJ_DEADLINE | + 0, .open = msm_open, .postclose = msm_postclose, .lastclose = drm_fb_helper_lastclose, diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c index 56641408ea74..51b461f32103 100644 --- a/drivers/gpu/drm/msm/msm_fence.c +++ b/drivers/gpu/drm/msm/msm_fence.c @@ -8,6 +8,35 @@
#include "msm_drv.h" #include "msm_fence.h" +#include "msm_gpu.h" + +static struct msm_gpu *fctx2gpu(struct msm_fence_context *fctx) +{ + struct msm_drm_private *priv = fctx->dev->dev_private; + return priv->gpu; +} + +static enum hrtimer_restart deadline_timer(struct hrtimer *t) +{ + struct msm_fence_context *fctx = container_of(t, + struct msm_fence_context, deadline_timer); + + kthread_queue_work(fctx2gpu(fctx)->worker, &fctx->deadline_work); + + return HRTIMER_NORESTART; +} + +static void deadline_work(struct kthread_work *work) +{ + struct msm_fence_context *fctx = container_of(work, + struct msm_fence_context, deadline_work); + + /* If deadline fence has already passed, nothing to do: */ + if (msm_fence_completed(fctx, fctx->next_deadline_fence)) + return; + + msm_devfreq_boost(fctx2gpu(fctx), 2); +}
struct msm_fence_context * @@ -36,6 +65,13 @@ msm_fence_context_alloc(struct drm_device *dev, volatile uint32_t *fenceptr, fctx->completed_fence = fctx->last_fence; *fctx->fenceptr = fctx->last_fence;
+ hrtimer_init(&fctx->deadline_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); + fctx->deadline_timer.function = deadline_timer; + + kthread_init_work(&fctx->deadline_work, deadline_work); + + fctx->next_deadline = ktime_get(); + return fctx; }
@@ -62,6 +98,8 @@ void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence) spin_lock_irqsave(&fctx->spinlock, flags); if (fence_after(fence, fctx->completed_fence)) fctx->completed_fence = fence; + if (msm_fence_completed(fctx, fctx->next_deadline_fence)) + hrtimer_cancel(&fctx->deadline_timer); spin_unlock_irqrestore(&fctx->spinlock, flags); }
@@ -92,10 +130,46 @@ static bool msm_fence_signaled(struct dma_fence *fence) return msm_fence_completed(f->fctx, f->base.seqno); }
+static void msm_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + struct msm_fence *f = to_msm_fence(fence); + struct msm_fence_context *fctx = f->fctx; + unsigned long flags; + ktime_t now; + + spin_lock_irqsave(&fctx->spinlock, flags); + now = ktime_get(); + + if (ktime_after(now, fctx->next_deadline) || + ktime_before(deadline, fctx->next_deadline)) { + fctx->next_deadline = deadline; + fctx->next_deadline_fence = + max(fctx->next_deadline_fence, (uint32_t)fence->seqno); + + /* + * Set timer to trigger boost 3ms before deadline, or + * if we are already less than 3ms before the deadline + * schedule boost work immediately. + */ + deadline = ktime_sub(deadline, ms_to_ktime(3)); + + if (ktime_after(now, deadline)) { + kthread_queue_work(fctx2gpu(fctx)->worker, + &fctx->deadline_work); + } else { + hrtimer_start(&fctx->deadline_timer, deadline, + HRTIMER_MODE_ABS); + } + } + + spin_unlock_irqrestore(&fctx->spinlock, flags); +} + static const struct dma_fence_ops msm_fence_ops = { .get_driver_name = msm_fence_get_driver_name, .get_timeline_name = msm_fence_get_timeline_name, .signaled = msm_fence_signaled, + .set_deadline = msm_fence_set_deadline, };
struct dma_fence * diff --git a/drivers/gpu/drm/msm/msm_fence.h b/drivers/gpu/drm/msm/msm_fence.h index 7f1798c54cd1..cdaebfb94f5c 100644 --- a/drivers/gpu/drm/msm/msm_fence.h +++ b/drivers/gpu/drm/msm/msm_fence.h @@ -52,6 +52,26 @@ struct msm_fence_context { volatile uint32_t *fenceptr;
spinlock_t spinlock; + + /* + * TODO this doesn't really deal with multiple deadlines, like + * if userspace got multiple frames ahead.. OTOH atomic updates + * don't queue, so maybe that is ok + */ + + /** next_deadline: Time of next deadline */ + ktime_t next_deadline; + + /** + * next_deadline_fence: + * + * Fence value for next pending deadline. The deadline timer is + * canceled when this fence is signaled. + */ + uint32_t next_deadline_fence; + + struct hrtimer deadline_timer; + struct kthread_work deadline_work; };
struct msm_fence_context * msm_fence_context_alloc(struct drm_device *dev,
From: Rob Clark robdclark@chromium.org
Signed-off-by: Rob Clark robdclark@chromium.org ---
This should probably be re-written by someone who knows the i915 request/timeline stuff better, to deal with non-immediate deadlines. But as-is I think this should be enough to handle the case where we want syncobj waits to trigger boost.
drivers/gpu/drm/i915/i915_driver.c | 2 +- drivers/gpu/drm/i915/i915_request.c | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c index cf1c0970ecb4..bd40b7bcb38a 100644 --- a/drivers/gpu/drm/i915/i915_driver.c +++ b/drivers/gpu/drm/i915/i915_driver.c @@ -1781,7 +1781,7 @@ static const struct drm_driver i915_drm_driver = { .driver_features = DRIVER_GEM | DRIVER_RENDER | DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_SYNCOBJ | - DRIVER_SYNCOBJ_TIMELINE, + DRIVER_SYNCOBJ_TIMELINE | DRIVER_SYNCOBJ_DEADLINE, .release = i915_driver_release, .open = i915_driver_open, .lastclose = i915_driver_lastclose, diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 7503dcb9043b..44491e7e214c 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -97,6 +97,25 @@ static bool i915_fence_enable_signaling(struct dma_fence *fence) return i915_request_enable_breadcrumb(to_request(fence)); }
+static void i915_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{ + struct i915_request *rq = to_request(fence); + + if (i915_request_completed(rq)) + return; + + if (i915_request_started(rq)) + return; + + /* + * TODO something more clever for deadlines that are in the + * future. I think probably track the nearest deadline in + * rq->timeline and set timer to trigger boost accordingly? + */ + + intel_rps_boost(rq); +} + static signed long i915_fence_wait(struct dma_fence *fence, bool interruptible, signed long timeout) @@ -182,6 +201,7 @@ const struct dma_fence_ops i915_fence_ops = { .signaled = i915_fence_signaled, .wait = i915_fence_wait, .release = i915_fence_release, + .set_deadline = i915_fence_set_deadline, };
static void irq_execute_cb(struct irq_work *wrk)
On 18/02/2023 21:15, Rob Clark wrote:
From: Rob Clark robdclark@chromium.org
Signed-off-by: Rob Clark robdclark@chromium.org
This should probably be re-written by someone who knows the i915 request/timeline stuff better, to deal with non-immediate deadlines. But as-is I think this should be enough to handle the case where we want syncobj waits to trigger boost.
Yeah, there are endless possibilities. :) But I think it is effectively similar enough to current waitboosting (when waits are done using the i915 specific ioctl). So as a first step I'll try to organize some internal power and performance testing, at least Chromebook focused, to see if modern userspace (syncobj based) even benefits and does not by some chance regress over the board.
Regards,
Tvrtko
drivers/gpu/drm/i915/i915_driver.c | 2 +- drivers/gpu/drm/i915/i915_request.c | 20 ++++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c index cf1c0970ecb4..bd40b7bcb38a 100644 --- a/drivers/gpu/drm/i915/i915_driver.c +++ b/drivers/gpu/drm/i915/i915_driver.c @@ -1781,7 +1781,7 @@ static const struct drm_driver i915_drm_driver = { .driver_features = DRIVER_GEM | DRIVER_RENDER | DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_SYNCOBJ |
DRIVER_SYNCOBJ_TIMELINE,
DRIVER_SYNCOBJ_TIMELINE | DRIVER_SYNCOBJ_DEADLINE,diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 7503dcb9043b..44491e7e214c 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -97,6 +97,25 @@ static bool i915_fence_enable_signaling(struct dma_fence *fence) return i915_request_enable_breadcrumb(to_request(fence)); } +static void i915_fence_set_deadline(struct dma_fence *fence, ktime_t deadline) +{
- struct i915_request *rq = to_request(fence);
- if (i915_request_completed(rq))
return;- if (i915_request_started(rq))
return;- /*
* TODO something more clever for deadlines that are in the* future. I think probably track the nearest deadline in* rq->timeline and set timer to trigger boost accordingly?*/- intel_rps_boost(rq);
+}
- static signed long i915_fence_wait(struct dma_fence *fence, bool interruptible, signed long timeout)
@@ -182,6 +201,7 @@ const struct dma_fence_ops i915_fence_ops = { .signaled = i915_fence_signaled, .wait = i915_fence_wait, .release = i915_fence_release,
- .set_deadline = i915_fence_set_deadline, };
static void irq_execute_cb(struct irq_work *wrk)
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Christian König -
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Rob Clark -
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Tvrtko Ursulin