[PATCH 1/9] drm/amdgpu: generally allow over-commit during BO allocation

[Felix Kuehling]

On 2022-11-25 05:21, Christian König wrote:
> We already fallback to a dummy BO with no backing store when we
> allocate GDS,GWS and OA resources and to GTT when we allocate VRAM.
>
> Drop all those workarounds and generalize this for GTT as well. This
> fixes ENOMEM issues with runaway applications which try to allocate/free
> GTT in a loop and are otherwise only limited by the CPU speed.
>
> The CS will wait for the cleanup of freed up BOs to satisfy the
> various domain specific limits and so effectively throttle those
> buggy applications down to a sane allocation behavior again.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>

This patch causes some regressions in KFDTest. KFDMemoryTest.MMBench 
sees a huge VRAM allocation slow-down. And 
KFDMemoryTest.LargestVramBufferTest can only allocate half the available 
memory.

This seems to be caused by initially validating VRAM BOs in the CPU 
domain, which allocates a ttm_tt. A subsequent validation in the VRAM 
domain involves a copy from GTT to VRAM.

After that, freeing of BOs can get delayed by the ghost object of a 
previous migration, which delays calling release notifiers and causes 
problems for KFDs available memory accounting.

I experimented with a workaround that validates BOs immediately after 
allocation, but that only moves around the delays and doesn't solve the 
problem. During those experiments I may also have stumbled over a bug in 
ttm_buffer_object_transfer: It calls ttm_bo_set_bulk_move before 
initializing and locking fbo->base.base._resv. This results in a flood 
of warnings because ttm_bo_set_bulk_move expects the reservation to be 
locked.

Right now I'd like to remove the bp.domain = initial_domain | 
AMDGPU_GEM_DOMAIN_CPU change in amdgpu_gem_object_create to fix this.

Regards,
   Felix


> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c    | 16 +++-------------
>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c |  6 +-----
>   2 files changed, 4 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index a0780a4e3e61..62e98f1ad770 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -113,7 +113,7 @@ int amdgpu_gem_object_create(struct amdgpu_device *adev, unsigned long size,
>   	bp.resv = resv;
>   	bp.preferred_domain = initial_domain;
>   	bp.flags = flags;
> -	bp.domain = initial_domain;
> +	bp.domain = initial_domain | AMDGPU_GEM_DOMAIN_CPU;
>   	bp.bo_ptr_size = sizeof(struct amdgpu_bo);
>   
>   	r = amdgpu_bo_create_user(adev, &bp, &ubo);
> @@ -332,20 +332,10 @@ int amdgpu_gem_create_ioctl(struct drm_device *dev, void *data,
>   	}
>   
>   	initial_domain = (u32)(0xffffffff & args->in.domains);
> -retry:
>   	r = amdgpu_gem_object_create(adev, size, args->in.alignment,
> -				     initial_domain,
> -				     flags, ttm_bo_type_device, resv, &gobj);
> +				     initial_domain, flags, ttm_bo_type_device,
> +				     resv, &gobj);
>   	if (r && r != -ERESTARTSYS) {
> -		if (flags & AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED) {
> -			flags &= ~AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
> -			goto retry;
> -		}
> -
> -		if (initial_domain == AMDGPU_GEM_DOMAIN_VRAM) {
> -			initial_domain |= AMDGPU_GEM_DOMAIN_GTT;
> -			goto retry;
> -		}
>   		DRM_DEBUG("Failed to allocate GEM object (%llu, %d, %llu, %d)\n",
>   				size, initial_domain, args->in.alignment, r);
>   	}
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index 974e85d8b6cc..919bbea2e3ac 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -581,11 +581,7 @@ int amdgpu_bo_create(struct amdgpu_device *adev,
>   		bo->flags |= AMDGPU_GEM_CREATE_VRAM_WIPE_ON_RELEASE;
>   
>   	bo->tbo.bdev = &adev->mman.bdev;
> -	if (bp->domain & (AMDGPU_GEM_DOMAIN_GWS | AMDGPU_GEM_DOMAIN_OA |
> -			  AMDGPU_GEM_DOMAIN_GDS))
> -		amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_CPU);
> -	else
> -		amdgpu_bo_placement_from_domain(bo, bp->domain);
> +	amdgpu_bo_placement_from_domain(bo, bp->domain);
>   	if (bp->type == ttm_bo_type_kernel)
>   		bo->tbo.priority = 1;
>