Op 28-09-12 22:10, Thomas Hellstrom schreef:
On 09/28/2012 09:42 PM, Thomas Hellstrom wrote:
On 09/28/2012 04:14 PM, Maarten Lankhorst wrote:
Hey,
Op 28-09-12 14:41, Maarten Lankhorst schreef:
Documentation says that code requiring dma-buf should add it to select, so inline fallbacks are not going to be used. A link error will make it obvious what went wrong, instead of silently doing nothing at runtime.
The whole patch series is in my tree, I use stg so things might move around, do not use for merging currently:
http://cgit.freedesktop.org/~mlankhorst/linux/log/?h=v10-wip
It contains everything in here plus the patches for ttm to make it work, I use a old snapshot of drm-next + merge of nouveau as base. Description of what the parts do:
Series to fix small api issues when moving over:
drm/ttm: Remove cpu_writers related code drm/ttm: Add ttm_bo_is_reserved function drm/radeon: Use ttm_bo_is_reserved drm/vmwgfx: use ttm_bo_is_reserved
drm/vmwgfx: remove use of fence_obj_args drm/ttm: remove sync_obj_arg drm/ttm: remove sync_obj_arg from ttm_bo_move_accel_cleanup drm/ttm: remove sync_arg entirely
drm/nouveau: unpin buffers before releasing to prevent lockdep warnings drm/nouveau: add reservation to nouveau_bo_vma_del drm/nouveau: add reservation to nouveau_gem_ioctl_cpu_prep
Hey great, now we only have one user left for fence waiting before reserving, lets fix that and remove fence lock: ttm_bo_cleanup_refs_or_queue and ttm_bo_cleanup_refs have to reserve before waiting, lets do it in the squash commit so we don't have to throw lock order around everywhere:
drm/ttm: remove fence_lock
-- Up to this point should be mergeable now
Then we start working on lru_lock removal slightly, this means the lru list no longer is empty but can contain only reserved buffers:
drm/ttm: do not check if list is empty in ttm_bo_force_list_clean drm/ttm: move reservations for ttm_bo_cleanup_refs
-- Still mergeable up to this point, just fixes
Patch series from this email: dma-buf: remove fallback for !CONFIG_DMA_SHARED_BUFFER fence: dma-buf cross-device synchronization (v9) seqno-fence: Hardware dma-buf implementation of fencing (v3) reservation: cross-device reservation support reservation: Add lockdep annotation and selftests
Now hook it up to drm/ttm in a few steps: usage around reservations: drm/ttm: make ttm reservation calls behave like reservation calls drm/ttm: use dma_reservation api dma-buf: use reservations drm/ttm: allow drivers to pass custom dma_reservation_objects for a bo
then kill off the lru lock around reservation: drm/ttm: remove lru_lock around ttm_bo_reserve drm/ttm: simplify ttm_eu_*
The lru_lock removal patch removes the lock around lru_lock around the reservation, this will break the assumption that items on the lru list and swap list can always be reserved, and this gets patched up too. Is there any part in ttm you disagree with? I believe that this is all mergeable, the lru_lock removal patch could be moved to before the reservation parts, this might make merging easier, but I don't think there is any ttm part of the series that are wrong on a conceptual level.
~Maarten
....From another email
As previously discussed, I'm unfortunately not prepared to accept removal of the reserve-lru atomicity into the TTM code at this point. The current code is based on this assumption and removing it will end up with efficiencies, breaking the delayed delete code and probably a locking nightmare when trying to write new TTM code.
The lru lock removal patch fixed the delayed delete code, it really is not different from the current situation. In fact it is more clear without the guarantee what various parts are trying to protect.
Nothing prevents you from holding the lru_lock while trylocking,
[1] While this would not cause any deadlocks, Any decent lockdep code would establish lru->reserve as the locking order once a lru- reserve trylock succeeds, but the locking order is really reserve->lru for obvious reasons, which means we will get a lot of lockdep errors? Yes, there are a two reversals like these already in the TTM code, and I'm not very proud of them.
leaving that guarantee intact for that part. Can you really just review the patch and tell me where it breaks and/or makes the code unreadable?
OK. Now I'm looking at http://cgit.freedesktop.org/~mlankhorst/linux/tree/drivers/gpu/drm/ttm/ttm_b...
And let's start with a function that's seen some change, ttm_mem_evict_first:
*) Line 715: You're traversing a list using list_for_each() calling a function that may remove the list entr||||y *) Line 722: You're unlocking the lock protecting the list in the middle of list traversal
*) Line 507: WARN_ON_ONCE in a code path quite likely to get called?
When will it get called? ttm_bo_delayed_delete calls it if it's already on delayed destroy list. ttm_mem_evict_first only calls it if on that list too. ttm_bo_swapout won't call it either if not on the list.
*) Line 512: sleep while atomic
Oops. Order is wrong, ttm_bo_wait has to be called first before anything else. Thanks for catching it.
*) Line 729: Forgot to unreserve
Thanks for catching it.
*) Line 740: Deadlocking reserve
Agreed, I'll remove it and just give up if no buffer could be reserved from the lru list. I was just confused since that function passed on no_wait_reserve which doesn't make sense there.
*) Line 757: Calling TTM Bo evict, but there might have been another process already evicting the buffer while you released the lru_lock in line 739, before reserving the buffer.
Yeah I think this part of the code needs to be taken out, which would be more similar to the old behavior since before nothing on the lru list was going to be contended anyway. Removing the offending code and just returning -EBUSY regardless should be the correct fix, maintaining the current behavior.
I'll remove the no_wait_reserve argument too, since it was unused before and would just be confusing to keep.
Actually, Lines 715, 722, 730 and 735 are OK, sorry about that, but the others should be valid. /Thomas
Is there any point in keeping ttm_bo_move_ttm's no_wait_reserve and no_wait_gpu argument? Nothing seems to use it and it would allow removal of 1 or more of those parameters for a whole lot of functions:
ttm_bo_move*, ttm_bo_handle_move_mem, ttm_bo_evict (though keeping no_wait_gpu), ttm_mem_evict_first, ttm_bo_mem_force_space, ttm_bo_mem_space, ttm_bo_move_buffer, ttm_bo_validate.
This would be a separate patch prerequisite patch though, but it should make it more clear that there's no blocking on reservation in eviction.
~Maarten