On Fri, May 17, 2024 at 3:41 AM Tvrtko Ursulin <tvrtko.ursu...@igalia.com> wrote: > > > On 16/05/2024 20:21, Alex Deucher wrote: > > On Thu, May 16, 2024 at 8:18 AM Tvrtko Ursulin <tursu...@igalia.com> wrote: > >> > >> From: Tvrtko Ursulin <tvrtko.ursu...@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. > > > > For APUs at least, we should never migrate because GTT and VRAM are > > both system memory so are effectively equal performance-wise. Maybe > > I was curious about this but thought there could be a reason why VRAM > carve-out is a fix small-ish size. It cannot be made 1:1 with RAM or > some other solution?
It's really only needed for displays at boot up prior to the OS loading or for displays on older APU that did not support scatter/gather display. The problem with increasing the carveout size is that that prevents the memory from being available to the rest of the system. Alex > > > this regressed when Christian reworked ttm to better handle migrating > > buffers back to VRAM after suspend on dGPUs? > > I will leave this to Christian to answer but for what this series is > concerned I'd say it is orthogonal to that. > > Here we have two fixes not limited to APU use cases, just so it happens > fixing the migration throttling improves things there too. And that even > despite the first patch which triggering *more* migration attempts. > Because the second patch then correctly curbs them. > > First patch should help with transient overcommit on discrete, allowing > things get back into VRAM as soon as there is space. > > Second patch tries to makes migration throttling work as intended. > > Volunteers for testing on discrete? :) > > >> > >> 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 > > Hmm! s/because/before/ here obviously! > > 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.koe...@amd.com> > >> Cc: Friedrich Vock <friedrich.v...@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(-) > >> > >> -- > >> 2.44.0 > >>
