[RFC v2 0/2] Discussion around eviction improvements

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>

Reduced re-spin of my previous series after Christian corrected a few
misconceptions that I had. So lets see if what remains makes sense or is still
misguided.

To summarise, the series address the following two issues:

 * Migration rate limiting does not work, at least not for the common case
   where userspace configures VRAM+GTT. It thinks it can stop migration attempts
   by playing with bo->allowed_domains vs bo->preferred domains but, both from
   the code, and from empirical experiments, I see that not working at all. When
   both masks are identical fiddling with them achieves nothing. Even when they
   are not identical allowed has a fallback GTT placement which means that when
   over the migration budget ttm_bo_validate with bo->allowed_domains can cause
   migration from GTT to VRAM.

 * Driver thinks it will be re-validating evicted buffers on the next submission
   but it does not for the very common case of VRAM+GTT because it only checks
   if current placement is *none* of the preferred placements.

These two patches appear to have a positive result for a memory intensive game
like Assassin's Creed Valhalla. On an APU like Steam Deck the game has a working
set around 5 GiB, while the VRAM is configured to 1 GiB. Correctly respecting
the migration budget appears to keep buffer blits at bay and improves the
minimum frame rate, ie. makes things smoother.

>From the game's built-in benchmark, average of three runs each:

						FPS
		migrated KiB	min	avg	max	min-1%	min-0.1%
  because	   20784781	10.00  37.00   89.67    22.00    12.33
  patched	    4227688	13.67  37.00   81.33    23.33    15.00

Disclaimers that I have is that more runs would be needed to be more confident
about the results. And more games. And APU versus discrete.

Cc: Christian König <christian.koenig at amd.com>
Cc: Friedrich Vock <friedrich.vock at gmx.de>

Tvrtko Ursulin (2):
  drm/amdgpu: Re-validate evicted buffers
  drm/amdgpu: Actually respect buffer migration budget

 drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 112 +++++++++++++++++++------
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c |  21 ++++-
 2 files changed, 103 insertions(+), 30 deletions(-)

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2.44.0