[RFC v2 0/2] Discussion around eviction improvements

[Tvrtko Ursulin]

Hi,

On 16/05/2024 13:18, Tvrtko Ursulin wrote:
> 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

Any feedback on this series?

As described above, neither migration rate limiting or re-validation of 
evicted buffers seems to work as expected currently.

Regards,

Tvrtko

> 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(-)
>