On Mon, May 15, 2023 at 10:42 AM Alex Deucher <alexdeucher@xxxxxxxxx> wrote: > > On Thu, May 11, 2023 at 9:38 PM Linus Lüssing <linus.luessing@xxxxxxxxx> wrote: > > > > Hi, > > > > Initially noticed this in some games, which seem to be a bit lazy > > with their VRAM allocations + freeing, that performance would drop > > dramatically / become unusable once the VRAM is full and GTT gets > > used. For instance in No Man's Sky after jumping a solar system > > or on DCS World on several maps and in multiplayer. I'm using an > > ATI/AMD Radeon RX 6650 XT, 8GB VRAM with an eGPU enclosure > > (Razer Core X Chroma, Thunderbolt 3), connected via a 40Gbit/s > > USB4 port. Which usually has great performance, until I hit the > > VRAM limit. > > > > I scripted some further tests and benchmarking around > > memmtest_vulkan(*) and these were the results: > > > > https://github.com/T-X/linux-amdgpu-radeon-vram-swapping-test/ > > > > I would have expected roughly the same speeds in all tests. > > However tests 5) and 6) yielded significantly lower performance. > > > > Which leads me to the conclusion that anything that gets allocated > > on GTT stays there and is never unswapped from GTT / system memory > > back to VRAM? > > It will get swapped back to VRAM if it makes sense for performance. > The driver throttles swapping if there is too much contention to avoid > the overhead of swapping large amounts of memory back and forth > between vram and gtt for every command submission. RADV also dynamically prefers GTT if you are using an eGPU and memory is contended: https://cgit.freedesktop.org/mesa/mesa/commit/?id=95d06343c693aa12b4cda5cda31d81fae138b0ec Alex > > Alex > > > > > I also read that there was some rework with a new TTM allocator > > in 2020. But dynamic (un)swapping via TTM seems currently unused? > > Is this expected? > > > > Regards, Linus > > > > (*): https://github.com/GpuZelenograd/memtest_vulkan
