Re: [PATCH] drm/amdkfd: Fix dmabuf's redundant eviction when unmapping

[Felix Kuehling <felix.kuehling@amd.com>]

If we keep the BO in the GTT domain, it means it will not be updated if 
we validate it again later in kfd_mem_dmamap_dmabuf. This means we'll 
use stale DMA addresses when we update the page tables after evictions.

I think we'll need to find a different way to avoid triggering the 
eviction fence on the original BO when changing the placement of the 
DMABuf import here. If you need help brainstorming here, please share a 
backtrace from the eviction generated with the debug_evictions module param.

Regards,
   Felix


Am 2023-04-03 um 13:59 schrieb Eric Huang:
> dmabuf is allocated/mapped as GTT domain, when dma-unmapping dmabuf
> changing placement to CPU will trigger memory eviction after calling
> ttm_bo_validate, and the eviction will cause performance drop.
> Keeping the correct domain will solve the issue.
>
> Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index a3b09edfd1bf..17b708acb447 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -642,7 +642,7 @@ kfd_mem_dmaunmap_dmabuf(struct kfd_mem_attachment *attachment)
>   	struct ttm_operation_ctx ctx = {.interruptible = true};
>   	struct amdgpu_bo *bo = attachment->bo_va->base.bo;
>   
> -	amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_CPU);
> +	amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_GTT);
>   	ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
>   }
>