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Re: [PATCH] drm/sched: Document run_job() refcount hazard

by Christian König

Am 20.12.24 um 13:45 schrieb Philipp Stanner: > From: Philipp Stanner <pstanner(a)redhat.com> > > drm_sched_backend_ops.run_job() returns a dma_fence for the scheduler. > That fence is signalled by the driver once the hardware completed the > associated job. The scheduler does not increment the reference count on > that fence, but implicitly expects to inherit this fence from run_job(). > > This is relatively subtle and prone to misunderstandings. > > This implies that, to keep a reference for itself, a driver needs to > call dma_fence_get() in addition to dma_fence_init() in that callback. > > It's further complicated by the fact that the scheduler even decrements > the refcount in drm_sched_run_job_work() since it created a new > reference in drm_sched_fence_scheduled(). It does, however, still use > its pointer to the fence after calling dma_fence_put() - which is safe > because of the aforementioned new reference, but actually still violates > the refcounting rules. > > Improve the explanatory comment for that decrement. > > Move the call to dma_fence_put() to the position behind the last usage > of the fence. > > Document the necessity to increment the reference count in > drm_sched_backend_ops.run_job(). > > Cc: Christian König <christian.koenig(a)amd.com> > Cc: Tvrtko Ursulin <tursulin(a)ursulin.net> > Cc: Andrey Grodzovsky <andrey.grodzovsky(a)amd.com> > Signed-off-by: Philipp Stanner <pstanner(a)redhat.com> > --- > drivers/gpu/drm/scheduler/sched_main.c | 10 +++++++--- > include/drm/gpu_scheduler.h | 20 ++++++++++++++++---- > 2 files changed, 23 insertions(+), 7 deletions(-) > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c > index 7ce25281c74c..d6f8df39d848 100644 > --- a/drivers/gpu/drm/scheduler/sched_main.c > +++ b/drivers/gpu/drm/scheduler/sched_main.c > @@ -1218,15 +1218,19 @@ static void drm_sched_run_job_work(struct work_struct *w) > drm_sched_fence_scheduled(s_fence, fence); > > if (!IS_ERR_OR_NULL(fence)) { > - /* Drop for original kref_init of the fence */ > - dma_fence_put(fence); > - > r = dma_fence_add_callback(fence, &sched_job->cb, > drm_sched_job_done_cb); > if (r == -ENOENT) > drm_sched_job_done(sched_job, fence->error); > else if (r) > DRM_DEV_ERROR(sched->dev, "fence add callback failed (%d)\n", r); > + > + /* > + * s_fence took a new reference to fence in the call to > + * drm_sched_fence_scheduled() above. The reference passed by > + * run_job() above is now not needed any longer. Drop it. > + */ > + dma_fence_put(fence); > } else { > drm_sched_job_done(sched_job, IS_ERR(fence) ? > PTR_ERR(fence) : 0); > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h > index 95e17504e46a..a1f5c9a14278 100644 > --- a/include/drm/gpu_scheduler.h > +++ b/include/drm/gpu_scheduler.h > @@ -420,10 +420,22 @@ struct drm_sched_backend_ops { > struct drm_sched_entity *s_entity); > > /** > - * @run_job: Called to execute the job once all of the dependencies > - * have been resolved. This may be called multiple times, if > - * timedout_job() has happened and drm_sched_job_recovery() > - * decides to try it again. > + * @run_job: Called to execute the job once all of the dependencies > + * have been resolved. This may be called multiple times, if > + * timedout_job() has happened and drm_sched_job_recovery() decides to > + * try it again. Maybe we should improve that here as well while at it. That drm_sched_job_recovery() can call this multiple times actually goes against the dma_fence rules since drivers can't easily allocate a new HW fence. Something like "The deprecated drm_sched_job_recovery() function might call this again, but it is strongly advised to not be used because it violates dma_fence memory allocations rules." On the other hand can of course be a separate patch. > + * > + * @sched_job: the job to run > + * > + * Returns: dma_fence the driver must signal once the hardware has > + * completed the job ("hardware fence"). > + * > + * Note that the scheduler expects to 'inherit' its own reference to > + * this fence from the callback. It does not invoke an extra > + * dma_fence_get() on it. Consequently, this callback must return a > + * fence whose refcount is at least 2: One for the scheduler's > + * reference returned here, another one for the reference kept by the > + * driver. Well the driver actually doesn't need any extra reference. The scheduler just needs to guarantee that this reference isn't dropped before it is signaled. Regards, Christian. > */ > struct dma_fence *(*run_job)(struct drm_sched_job *sched_job); >

6 months, 1 week

[PATCH 6.1 633/772] dma-fence: Use kernels sort for merging fences

by Greg Kroah-Hartman

6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit fe52c649438b8489c9456681d93a9b3de3d38263 upstream. One alternative to the fix Christian proposed in https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@am… is to replace the rather complex open coded sorting loops with the kernel standard sort followed by a context squashing pass. Proposed advantage of this would be readability but one concern Christian raised was that there could be many fences, that they are typically mostly sorted, and so the kernel's heap sort would be much worse by the proposed algorithm. I had a look running some games and vkcube to see what are the typical number of input fences. Tested scenarios: 1) Hogwarts Legacy under Gamescope 450 calls per second to __dma_fence_unwrap_merge. Percentages per number of fences buckets, before and after checking for signalled status, sorting and flattening: N Before After 0 0.91% 1 69.40% 2-3 28.72% 9.4% (90.6% resolved to one fence) 4-5 0.93% 6-9 0.03% 10+ 2) Cyberpunk 2077 under Gamescope 1050 calls per second, amounting to 0.01% CPU time according to perf top. N Before After 0 1.13% 1 52.30% 2-3 40.34% 55.57% 4-5 1.46% 0.50% 6-9 2.44% 10+ 2.34% 3) vkcube under Plasma 90 calls per second. N Before After 0 1 2-3 100% 0% (Ie. all resolved to a single fence) 4-5 6-9 10+ In the case of vkcube all invocations in the 2-3 bucket were actually just two input fences. >From these numbers it looks like the heap sort should not be a disadvantage, given how the dominant case is <= 2 input fences which heap sort solves with just one compare and swap. (And for the case of one input fence we have a fast path in the previous patch.) A complementary possibility is to implement a different sorting algorithm under the same API as the kernel's sort() and so keep the simplicity, potentially moving the new sort under lib/ if it would be found more widely useful. v2: * Hold on to fence references and reduce commentary. (Christian) * Record and use latest signaled timestamp in the 2nd loop too. * Consolidate zero or one fences fast paths. v3: * Reverse the seqno sort order for a simpler squashing pass. (Christian) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617 Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 128 ++++++++++++++--------------- 1 file changed, 61 insertions(+), 67 deletions(-) diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c index b19d0adf6086..6345062731f1 100644 --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -12,6 +12,7 @@ #include <linux/dma-fence-chain.h> #include <linux/dma-fence-unwrap.h> #include <linux/slab.h> +#include <linux/sort.h> /* Internal helper to start new array iteration, don't use directly */ static struct dma_fence * @@ -59,6 +60,25 @@ struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor) } EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); + +static int fence_cmp(const void *_a, const void *_b) +{ + struct dma_fence *a = *(struct dma_fence **)_a; + struct dma_fence *b = *(struct dma_fence **)_b; + + if (a->context < b->context) + return -1; + else if (a->context > b->context) + return 1; + + if (dma_fence_is_later(b, a)) + return 1; + else if (dma_fence_is_later(a, b)) + return -1; + + return 0; +} + /* Implementation for the dma_fence_merge() marco, don't use directly */ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence **fences, @@ -67,8 +87,7 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence_array *result; struct dma_fence *tmp, **array; ktime_t timestamp; - unsigned int i; - size_t count; + int i, j, count; count = 0; timestamp = ns_to_ktime(0); @@ -96,80 +115,55 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, if (!array) return NULL; - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; + for (i = 0; i < num_fences; ++i) { + dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { + if (!dma_fence_is_signaled(tmp)) { + array[count++] = dma_fence_get(tmp); } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; + ktime_t t = dma_fence_timestamp(tmp); + + if (ktime_after(t, timestamp)) + timestamp = t; } } - - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); - - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; } - if (count == 1) { - tmp = array[0]; - goto return_tmp; - } + if (count == 0 || count == 1) + goto return_fastpath; - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - for (i = 0; i < count; i++) + sort(array, count, sizeof(*array), fence_cmp, NULL); + + /* + * Only keep the most recent fence for each context. + */ + j = 0; + for (i = 1; i < count; i++) { + if (array[i]->context == array[j]->context) dma_fence_put(array[i]); - tmp = NULL; - goto return_tmp; + else + array[++j] = array[i]; } - return &result->base; + count = ++j; + + if (count > 1) { + result = dma_fence_array_create(count, array, + dma_fence_context_alloc(1), + 1, false); + if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); + tmp = NULL; + goto return_tmp; + } + return &result->base; + } + +return_fastpath: + if (count == 0) + tmp = dma_fence_allocate_private_stub(timestamp); + else + tmp = array[0]; return_tmp: kfree(array); -- 2.47.1

6 months, 2 weeks

[PATCH 6.1 632/772] dma-fence: Fix reference leak on fence merge failure path

by Greg Kroah-Hartman

6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit 949291c5314009b4f6e252391edbb40fdd5d5414 upstream. Release all fence references if the output dma-fence-array could not be allocated. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-2-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c index 628af51c81af..b19d0adf6086 100644 --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -164,6 +164,8 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, dma_fence_context_alloc(1), 1, false); if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); tmp = NULL; goto return_tmp; } -- 2.47.1

6 months, 2 weeks

[PATCH 6.6 175/356] dma-fence: Use kernels sort for merging fences

by Greg Kroah-Hartman

6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit fe52c649438b8489c9456681d93a9b3de3d38263 upstream. One alternative to the fix Christian proposed in https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@am… is to replace the rather complex open coded sorting loops with the kernel standard sort followed by a context squashing pass. Proposed advantage of this would be readability but one concern Christian raised was that there could be many fences, that they are typically mostly sorted, and so the kernel's heap sort would be much worse by the proposed algorithm. I had a look running some games and vkcube to see what are the typical number of input fences. Tested scenarios: 1) Hogwarts Legacy under Gamescope 450 calls per second to __dma_fence_unwrap_merge. Percentages per number of fences buckets, before and after checking for signalled status, sorting and flattening: N Before After 0 0.91% 1 69.40% 2-3 28.72% 9.4% (90.6% resolved to one fence) 4-5 0.93% 6-9 0.03% 10+ 2) Cyberpunk 2077 under Gamescope 1050 calls per second, amounting to 0.01% CPU time according to perf top. N Before After 0 1.13% 1 52.30% 2-3 40.34% 55.57% 4-5 1.46% 0.50% 6-9 2.44% 10+ 2.34% 3) vkcube under Plasma 90 calls per second. N Before After 0 1 2-3 100% 0% (Ie. all resolved to a single fence) 4-5 6-9 10+ In the case of vkcube all invocations in the 2-3 bucket were actually just two input fences. >From these numbers it looks like the heap sort should not be a disadvantage, given how the dominant case is <= 2 input fences which heap sort solves with just one compare and swap. (And for the case of one input fence we have a fast path in the previous patch.) A complementary possibility is to implement a different sorting algorithm under the same API as the kernel's sort() and so keep the simplicity, potentially moving the new sort under lib/ if it would be found more widely useful. v2: * Hold on to fence references and reduce commentary. (Christian) * Record and use latest signaled timestamp in the 2nd loop too. * Consolidate zero or one fences fast paths. v3: * Reverse the seqno sort order for a simpler squashing pass. (Christian) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617 Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 126 +++++++++++++++++-------------------- 1 file changed, 60 insertions(+), 66 deletions(-) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -12,6 +12,7 @@ #include <linux/dma-fence-chain.h> #include <linux/dma-fence-unwrap.h> #include <linux/slab.h> +#include <linux/sort.h> /* Internal helper to start new array iteration, don't use directly */ static struct dma_fence * @@ -59,6 +60,25 @@ struct dma_fence *dma_fence_unwrap_next( } EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); + +static int fence_cmp(const void *_a, const void *_b) +{ + struct dma_fence *a = *(struct dma_fence **)_a; + struct dma_fence *b = *(struct dma_fence **)_b; + + if (a->context < b->context) + return -1; + else if (a->context > b->context) + return 1; + + if (dma_fence_is_later(b, a)) + return 1; + else if (dma_fence_is_later(a, b)) + return -1; + + return 0; +} + /* Implementation for the dma_fence_merge() marco, don't use directly */ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence **fences, @@ -67,8 +87,7 @@ struct dma_fence *__dma_fence_unwrap_mer struct dma_fence_array *result; struct dma_fence *tmp, **array; ktime_t timestamp; - unsigned int i; - size_t count; + int i, j, count; count = 0; timestamp = ns_to_ktime(0); @@ -96,80 +115,55 @@ struct dma_fence *__dma_fence_unwrap_mer if (!array) return NULL; - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; + for (i = 0; i < num_fences; ++i) { + dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { + if (!dma_fence_is_signaled(tmp)) { + array[count++] = dma_fence_get(tmp); } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; + ktime_t t = dma_fence_timestamp(tmp); + + if (ktime_after(t, timestamp)) + timestamp = t; } } + } - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); + if (count == 0 || count == 1) + goto return_fastpath; - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } + sort(array, count, sizeof(*array), fence_cmp, NULL); - if (count == 1) { - tmp = array[0]; - goto return_tmp; + /* + * Only keep the most recent fence for each context. + */ + j = 0; + for (i = 1; i < count; i++) { + if (array[i]->context == array[j]->context) + dma_fence_put(array[i]); + else + array[++j] = array[i]; } + count = ++j; - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - for (i = 0; i < count; i++) - dma_fence_put(array[i]); - tmp = NULL; - goto return_tmp; + if (count > 1) { + result = dma_fence_array_create(count, array, + dma_fence_context_alloc(1), + 1, false); + if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); + tmp = NULL; + goto return_tmp; + } + return &result->base; } - return &result->base; + +return_fastpath: + if (count == 0) + tmp = dma_fence_allocate_private_stub(timestamp); + else + tmp = array[0]; return_tmp: kfree(array);

6 months, 2 weeks

[PATCH 6.6 174/356] dma-fence: Fix reference leak on fence merge failure path

by Greg Kroah-Hartman

6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit 949291c5314009b4f6e252391edbb40fdd5d5414 upstream. Release all fence references if the output dma-fence-array could not be allocated. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-2-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -164,6 +164,8 @@ restart: dma_fence_context_alloc(1), 1, false); if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); tmp = NULL; goto return_tmp; }

6 months, 2 weeks

[PATCH 6.12 187/466] dma-fence: Use kernels sort for merging fences

by Greg Kroah-Hartman

6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit fe52c649438b8489c9456681d93a9b3de3d38263 upstream. One alternative to the fix Christian proposed in https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@am… is to replace the rather complex open coded sorting loops with the kernel standard sort followed by a context squashing pass. Proposed advantage of this would be readability but one concern Christian raised was that there could be many fences, that they are typically mostly sorted, and so the kernel's heap sort would be much worse by the proposed algorithm. I had a look running some games and vkcube to see what are the typical number of input fences. Tested scenarios: 1) Hogwarts Legacy under Gamescope 450 calls per second to __dma_fence_unwrap_merge. Percentages per number of fences buckets, before and after checking for signalled status, sorting and flattening: N Before After 0 0.91% 1 69.40% 2-3 28.72% 9.4% (90.6% resolved to one fence) 4-5 0.93% 6-9 0.03% 10+ 2) Cyberpunk 2077 under Gamescope 1050 calls per second, amounting to 0.01% CPU time according to perf top. N Before After 0 1.13% 1 52.30% 2-3 40.34% 55.57% 4-5 1.46% 0.50% 6-9 2.44% 10+ 2.34% 3) vkcube under Plasma 90 calls per second. N Before After 0 1 2-3 100% 0% (Ie. all resolved to a single fence) 4-5 6-9 10+ In the case of vkcube all invocations in the 2-3 bucket were actually just two input fences. >From these numbers it looks like the heap sort should not be a disadvantage, given how the dominant case is <= 2 input fences which heap sort solves with just one compare and swap. (And for the case of one input fence we have a fast path in the previous patch.) A complementary possibility is to implement a different sorting algorithm under the same API as the kernel's sort() and so keep the simplicity, potentially moving the new sort under lib/ if it would be found more widely useful. v2: * Hold on to fence references and reduce commentary. (Christian) * Record and use latest signaled timestamp in the 2nd loop too. * Consolidate zero or one fences fast paths. v3: * Reverse the seqno sort order for a simpler squashing pass. (Christian) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617 Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 126 +++++++++++++++++-------------------- 1 file changed, 60 insertions(+), 66 deletions(-) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -12,6 +12,7 @@ #include <linux/dma-fence-chain.h> #include <linux/dma-fence-unwrap.h> #include <linux/slab.h> +#include <linux/sort.h> /* Internal helper to start new array iteration, don't use directly */ static struct dma_fence * @@ -59,6 +60,25 @@ struct dma_fence *dma_fence_unwrap_next( } EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); + +static int fence_cmp(const void *_a, const void *_b) +{ + struct dma_fence *a = *(struct dma_fence **)_a; + struct dma_fence *b = *(struct dma_fence **)_b; + + if (a->context < b->context) + return -1; + else if (a->context > b->context) + return 1; + + if (dma_fence_is_later(b, a)) + return 1; + else if (dma_fence_is_later(a, b)) + return -1; + + return 0; +} + /* Implementation for the dma_fence_merge() marco, don't use directly */ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence **fences, @@ -67,8 +87,7 @@ struct dma_fence *__dma_fence_unwrap_mer struct dma_fence_array *result; struct dma_fence *tmp, **array; ktime_t timestamp; - unsigned int i; - size_t count; + int i, j, count; count = 0; timestamp = ns_to_ktime(0); @@ -96,80 +115,55 @@ struct dma_fence *__dma_fence_unwrap_mer if (!array) return NULL; - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; + for (i = 0; i < num_fences; ++i) { + dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { + if (!dma_fence_is_signaled(tmp)) { + array[count++] = dma_fence_get(tmp); } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; + ktime_t t = dma_fence_timestamp(tmp); + + if (ktime_after(t, timestamp)) + timestamp = t; } } + } - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); + if (count == 0 || count == 1) + goto return_fastpath; - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } + sort(array, count, sizeof(*array), fence_cmp, NULL); - if (count == 1) { - tmp = array[0]; - goto return_tmp; + /* + * Only keep the most recent fence for each context. + */ + j = 0; + for (i = 1; i < count; i++) { + if (array[i]->context == array[j]->context) + dma_fence_put(array[i]); + else + array[++j] = array[i]; } + count = ++j; - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - for (i = 0; i < count; i++) - dma_fence_put(array[i]); - tmp = NULL; - goto return_tmp; + if (count > 1) { + result = dma_fence_array_create(count, array, + dma_fence_context_alloc(1), + 1, false); + if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); + tmp = NULL; + goto return_tmp; + } + return &result->base; } - return &result->base; + +return_fastpath: + if (count == 0) + tmp = dma_fence_allocate_private_stub(timestamp); + else + tmp = array[0]; return_tmp: kfree(array);

6 months, 2 weeks

[PATCH 6.12 186/466] dma-fence: Fix reference leak on fence merge failure path

by Greg Kroah-Hartman

6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit 949291c5314009b4f6e252391edbb40fdd5d5414 upstream. Release all fence references if the output dma-fence-array could not be allocated. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-2-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -164,6 +164,8 @@ restart: dma_fence_context_alloc(1), 1, false); if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); tmp = NULL; goto return_tmp; }

6 months, 2 weeks

Patch "dma-fence: Use kernel's sort for merging fences" has been added to the 6.12-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled dma-fence: Use kernel's sort for merging fences to the 6.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: dma-fence-use-kernel-s-sort-for-merging-fences.patch and it can be found in the queue-6.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. From fe52c649438b8489c9456681d93a9b3de3d38263 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Date: Fri, 15 Nov 2024 10:21:50 +0000 Subject: dma-fence: Use kernel's sort for merging fences MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit fe52c649438b8489c9456681d93a9b3de3d38263 upstream. One alternative to the fix Christian proposed in https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@am… is to replace the rather complex open coded sorting loops with the kernel standard sort followed by a context squashing pass. Proposed advantage of this would be readability but one concern Christian raised was that there could be many fences, that they are typically mostly sorted, and so the kernel's heap sort would be much worse by the proposed algorithm. I had a look running some games and vkcube to see what are the typical number of input fences. Tested scenarios: 1) Hogwarts Legacy under Gamescope 450 calls per second to __dma_fence_unwrap_merge. Percentages per number of fences buckets, before and after checking for signalled status, sorting and flattening: N Before After 0 0.91% 1 69.40% 2-3 28.72% 9.4% (90.6% resolved to one fence) 4-5 0.93% 6-9 0.03% 10+ 2) Cyberpunk 2077 under Gamescope 1050 calls per second, amounting to 0.01% CPU time according to perf top. N Before After 0 1.13% 1 52.30% 2-3 40.34% 55.57% 4-5 1.46% 0.50% 6-9 2.44% 10+ 2.34% 3) vkcube under Plasma 90 calls per second. N Before After 0 1 2-3 100% 0% (Ie. all resolved to a single fence) 4-5 6-9 10+ In the case of vkcube all invocations in the 2-3 bucket were actually just two input fences. From these numbers it looks like the heap sort should not be a disadvantage, given how the dominant case is <= 2 input fences which heap sort solves with just one compare and swap. (And for the case of one input fence we have a fast path in the previous patch.) A complementary possibility is to implement a different sorting algorithm under the same API as the kernel's sort() and so keep the simplicity, potentially moving the new sort under lib/ if it would be found more widely useful. v2: * Hold on to fence references and reduce commentary. (Christian) * Record and use latest signaled timestamp in the 2nd loop too. * Consolidate zero or one fences fast paths. v3: * Reverse the seqno sort order for a simpler squashing pass. (Christian) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617 Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 126 +++++++++++++++++-------------------- 1 file changed, 60 insertions(+), 66 deletions(-) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -12,6 +12,7 @@ #include <linux/dma-fence-chain.h> #include <linux/dma-fence-unwrap.h> #include <linux/slab.h> +#include <linux/sort.h> /* Internal helper to start new array iteration, don't use directly */ static struct dma_fence * @@ -59,6 +60,25 @@ struct dma_fence *dma_fence_unwrap_next( } EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); + +static int fence_cmp(const void *_a, const void *_b) +{ + struct dma_fence *a = *(struct dma_fence **)_a; + struct dma_fence *b = *(struct dma_fence **)_b; + + if (a->context < b->context) + return -1; + else if (a->context > b->context) + return 1; + + if (dma_fence_is_later(b, a)) + return 1; + else if (dma_fence_is_later(a, b)) + return -1; + + return 0; +} + /* Implementation for the dma_fence_merge() marco, don't use directly */ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence **fences, @@ -67,8 +87,7 @@ struct dma_fence *__dma_fence_unwrap_mer struct dma_fence_array *result; struct dma_fence *tmp, **array; ktime_t timestamp; - unsigned int i; - size_t count; + int i, j, count; count = 0; timestamp = ns_to_ktime(0); @@ -96,80 +115,55 @@ struct dma_fence *__dma_fence_unwrap_mer if (!array) return NULL; - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; + for (i = 0; i < num_fences; ++i) { + dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { + if (!dma_fence_is_signaled(tmp)) { + array[count++] = dma_fence_get(tmp); } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; + ktime_t t = dma_fence_timestamp(tmp); + + if (ktime_after(t, timestamp)) + timestamp = t; } } + } - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); + if (count == 0 || count == 1) + goto return_fastpath; - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } + sort(array, count, sizeof(*array), fence_cmp, NULL); - if (count == 1) { - tmp = array[0]; - goto return_tmp; + /* + * Only keep the most recent fence for each context. + */ + j = 0; + for (i = 1; i < count; i++) { + if (array[i]->context == array[j]->context) + dma_fence_put(array[i]); + else + array[++j] = array[i]; } + count = ++j; - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - for (i = 0; i < count; i++) - dma_fence_put(array[i]); - tmp = NULL; - goto return_tmp; + if (count > 1) { + result = dma_fence_array_create(count, array, + dma_fence_context_alloc(1), + 1, false); + if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); + tmp = NULL; + goto return_tmp; + } + return &result->base; } - return &result->base; + +return_fastpath: + if (count == 0) + tmp = dma_fence_allocate_private_stub(timestamp); + else + tmp = array[0]; return_tmp: kfree(array); Patches currently in stable-queue which might be from tvrtko.ursulin(a)igalia.com are queue-6.12/dma-fence-use-kernel-s-sort-for-merging-fences.patch queue-6.12/dma-buf-fix-dma_fence_array_signaled-v4.patch queue-6.12/dma-fence-fix-reference-leak-on-fence-merge-failure-path.patch

6 months, 2 weeks

Patch "dma-fence: Fix reference leak on fence merge failure path" has been added to the 6.12-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled dma-fence: Fix reference leak on fence merge failure path to the 6.12-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: dma-fence-fix-reference-leak-on-fence-merge-failure-path.patch and it can be found in the queue-6.12 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. From 949291c5314009b4f6e252391edbb40fdd5d5414 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Date: Fri, 15 Nov 2024 10:21:49 +0000 Subject: dma-fence: Fix reference leak on fence merge failure path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit 949291c5314009b4f6e252391edbb40fdd5d5414 upstream. Release all fence references if the output dma-fence-array could not be allocated. Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-2-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -164,6 +164,8 @@ restart: dma_fence_context_alloc(1), 1, false); if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); tmp = NULL; goto return_tmp; } Patches currently in stable-queue which might be from tvrtko.ursulin(a)igalia.com are queue-6.12/dma-fence-use-kernel-s-sort-for-merging-fences.patch queue-6.12/dma-buf-fix-dma_fence_array_signaled-v4.patch queue-6.12/dma-fence-fix-reference-leak-on-fence-merge-failure-path.patch

6 months, 2 weeks

Patch "dma-fence: Use kernel's sort for merging fences" has been added to the 6.6-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled dma-fence: Use kernel's sort for merging fences to the 6.6-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: dma-fence-use-kernel-s-sort-for-merging-fences.patch and it can be found in the queue-6.6 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. From fe52c649438b8489c9456681d93a9b3de3d38263 Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Date: Fri, 15 Nov 2024 10:21:50 +0000 Subject: dma-fence: Use kernel's sort for merging fences MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> commit fe52c649438b8489c9456681d93a9b3de3d38263 upstream. One alternative to the fix Christian proposed in https://lore.kernel.org/dri-devel/20241024124159.4519-3-christian.koenig@am… is to replace the rather complex open coded sorting loops with the kernel standard sort followed by a context squashing pass. Proposed advantage of this would be readability but one concern Christian raised was that there could be many fences, that they are typically mostly sorted, and so the kernel's heap sort would be much worse by the proposed algorithm. I had a look running some games and vkcube to see what are the typical number of input fences. Tested scenarios: 1) Hogwarts Legacy under Gamescope 450 calls per second to __dma_fence_unwrap_merge. Percentages per number of fences buckets, before and after checking for signalled status, sorting and flattening: N Before After 0 0.91% 1 69.40% 2-3 28.72% 9.4% (90.6% resolved to one fence) 4-5 0.93% 6-9 0.03% 10+ 2) Cyberpunk 2077 under Gamescope 1050 calls per second, amounting to 0.01% CPU time according to perf top. N Before After 0 1.13% 1 52.30% 2-3 40.34% 55.57% 4-5 1.46% 0.50% 6-9 2.44% 10+ 2.34% 3) vkcube under Plasma 90 calls per second. N Before After 0 1 2-3 100% 0% (Ie. all resolved to a single fence) 4-5 6-9 10+ In the case of vkcube all invocations in the 2-3 bucket were actually just two input fences. From these numbers it looks like the heap sort should not be a disadvantage, given how the dominant case is <= 2 input fences which heap sort solves with just one compare and swap. (And for the case of one input fence we have a fast path in the previous patch.) A complementary possibility is to implement a different sorting algorithm under the same API as the kernel's sort() and so keep the simplicity, potentially moving the new sort under lib/ if it would be found more widely useful. v2: * Hold on to fence references and reduce commentary. (Christian) * Record and use latest signaled timestamp in the 2nd loop too. * Consolidate zero or one fences fast paths. v3: * Reverse the seqno sort order for a simpler squashing pass. (Christian) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin(a)igalia.com> Fixes: 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3") Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3617 Cc: Christian König <christian.koenig(a)amd.com> Cc: Daniel Vetter <daniel.vetter(a)ffwll.ch> Cc: Sumit Semwal <sumit.semwal(a)linaro.org> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Friedrich Vock <friedrich.vock(a)gmx.de> Cc: linux-media(a)vger.kernel.org Cc: dri-devel(a)lists.freedesktop.org Cc: linaro-mm-sig(a)lists.linaro.org Cc: <stable(a)vger.kernel.org> # v6.0+ Reviewed-by: Christian König <christian.koenig(a)amd.com> Signed-off-by: Christian König <christian.koenig(a)amd.com> Link: https://patchwork.freedesktop.org/patch/msgid/20241115102153.1980-3-tursuli… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- drivers/dma-buf/dma-fence-unwrap.c | 126 +++++++++++++++++-------------------- 1 file changed, 60 insertions(+), 66 deletions(-) --- a/drivers/dma-buf/dma-fence-unwrap.c +++ b/drivers/dma-buf/dma-fence-unwrap.c @@ -12,6 +12,7 @@ #include <linux/dma-fence-chain.h> #include <linux/dma-fence-unwrap.h> #include <linux/slab.h> +#include <linux/sort.h> /* Internal helper to start new array iteration, don't use directly */ static struct dma_fence * @@ -59,6 +60,25 @@ struct dma_fence *dma_fence_unwrap_next( } EXPORT_SYMBOL_GPL(dma_fence_unwrap_next); + +static int fence_cmp(const void *_a, const void *_b) +{ + struct dma_fence *a = *(struct dma_fence **)_a; + struct dma_fence *b = *(struct dma_fence **)_b; + + if (a->context < b->context) + return -1; + else if (a->context > b->context) + return 1; + + if (dma_fence_is_later(b, a)) + return 1; + else if (dma_fence_is_later(a, b)) + return -1; + + return 0; +} + /* Implementation for the dma_fence_merge() marco, don't use directly */ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences, struct dma_fence **fences, @@ -67,8 +87,7 @@ struct dma_fence *__dma_fence_unwrap_mer struct dma_fence_array *result; struct dma_fence *tmp, **array; ktime_t timestamp; - unsigned int i; - size_t count; + int i, j, count; count = 0; timestamp = ns_to_ktime(0); @@ -96,80 +115,55 @@ struct dma_fence *__dma_fence_unwrap_mer if (!array) return NULL; - /* - * This trashes the input fence array and uses it as position for the - * following merge loop. This works because the dma_fence_merge() - * wrapper macro is creating this temporary array on the stack together - * with the iterators. - */ - for (i = 0; i < num_fences; ++i) - fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]); - count = 0; - do { - unsigned int sel; - -restart: - tmp = NULL; - for (i = 0; i < num_fences; ++i) { - struct dma_fence *next; - - while (fences[i] && dma_fence_is_signaled(fences[i])) - fences[i] = dma_fence_unwrap_next(&iter[i]); - - next = fences[i]; - if (!next) - continue; - - /* - * We can't guarantee that inpute fences are ordered by - * context, but it is still quite likely when this - * function is used multiple times. So attempt to order - * the fences by context as we pass over them and merge - * fences with the same context. - */ - if (!tmp || tmp->context > next->context) { - tmp = next; - sel = i; - - } else if (tmp->context < next->context) { - continue; - - } else if (dma_fence_is_later(tmp, next)) { - fences[i] = dma_fence_unwrap_next(&iter[i]); - goto restart; + for (i = 0; i < num_fences; ++i) { + dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) { + if (!dma_fence_is_signaled(tmp)) { + array[count++] = dma_fence_get(tmp); } else { - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - goto restart; + ktime_t t = dma_fence_timestamp(tmp); + + if (ktime_after(t, timestamp)) + timestamp = t; } } + } - if (tmp) { - array[count++] = dma_fence_get(tmp); - fences[sel] = dma_fence_unwrap_next(&iter[sel]); - } - } while (tmp); + if (count == 0 || count == 1) + goto return_fastpath; - if (count == 0) { - tmp = dma_fence_allocate_private_stub(ktime_get()); - goto return_tmp; - } + sort(array, count, sizeof(*array), fence_cmp, NULL); - if (count == 1) { - tmp = array[0]; - goto return_tmp; + /* + * Only keep the most recent fence for each context. + */ + j = 0; + for (i = 1; i < count; i++) { + if (array[i]->context == array[j]->context) + dma_fence_put(array[i]); + else + array[++j] = array[i]; } + count = ++j; - result = dma_fence_array_create(count, array, - dma_fence_context_alloc(1), - 1, false); - if (!result) { - for (i = 0; i < count; i++) - dma_fence_put(array[i]); - tmp = NULL; - goto return_tmp; + if (count > 1) { + result = dma_fence_array_create(count, array, + dma_fence_context_alloc(1), + 1, false); + if (!result) { + for (i = 0; i < count; i++) + dma_fence_put(array[i]); + tmp = NULL; + goto return_tmp; + } + return &result->base; } - return &result->base; + +return_fastpath: + if (count == 0) + tmp = dma_fence_allocate_private_stub(timestamp); + else + tmp = array[0]; return_tmp: kfree(array); Patches currently in stable-queue which might be from tvrtko.ursulin(a)igalia.com are queue-6.6/dma-fence-use-kernel-s-sort-for-merging-fences.patch queue-6.6/dma-buf-fix-dma_fence_array_signaled-v4.patch queue-6.6/dma-fence-fix-reference-leak-on-fence-merge-failure-path.patch

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