linux-kernel - Re: [PATCH v2 11/20] drm/amdgpu: round robin through clear_entities in amdgpu_fill

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Message-ID: <af0e47da-81ef-4247-ae10-52048d797291@amd.com>
Date: Mon, 17 Nov 2025 09:47:39 +0100
From: Christian König <christian.koenig@....com>
To: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>,
 Alex Deucher <alexander.deucher@....com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/20] drm/amdgpu: round robin through clear_entities
 in amdgpu_fill_buffer

On 11/13/25 17:05, Pierre-Eric Pelloux-Prayer wrote:
> This makes clear of different BOs run in parallel. Partial jobs to
> clear a single BO still execute sequentially.
> 
> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 2 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c    | 9 ++++++++-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h    | 1 +
>  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index be3532134e46..33b397107778 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -1321,7 +1321,7 @@ void amdgpu_bo_release_notify(struct ttm_buffer_object *bo)
>  	if (r)
>  		goto out;
>  
> -	r = amdgpu_fill_buffer(&adev->mman.clear_entities[0], abo, 0, &bo->base._resv,
> +	r = amdgpu_fill_buffer(NULL, abo, 0, &bo->base._resv,
>  			       &fence, NULL, AMDGPU_KERNEL_JOB_ID_CLEAR_ON_RELEASE);
>  	if (WARN_ON(r))
>  		goto out;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 411997db70eb..486c701d0d5b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -2224,6 +2224,7 @@ u32 amdgpu_ttm_set_buffer_funcs_status(struct amdgpu_device *adev, bool enable)
>  		adev->mman.clear_entities = kcalloc(num_clear_entities,
>  						    sizeof(struct amdgpu_ttm_buffer_entity),
>  						    GFP_KERNEL);
> +		atomic_set(&adev->mman.next_clear_entity, 0);
>  		if (!adev->mman.clear_entities)
>  			goto error_free_entity;
>  
> @@ -2489,7 +2490,7 @@ int amdgpu_fill_buffer(struct amdgpu_ttm_buffer_entity *entity,
>  	struct amdgpu_ring *ring = adev->mman.buffer_funcs_ring;
>  	struct dma_fence *fence = NULL;
>  	struct amdgpu_res_cursor dst;
> -	int r;
> +	int r, e;
>  
>  	if (!adev->mman.buffer_funcs_enabled) {
>  		dev_err(adev->dev,
> @@ -2497,6 +2498,12 @@ int amdgpu_fill_buffer(struct amdgpu_ttm_buffer_entity *entity,
>  		return -EINVAL;
>  	}
>  
> +	if (entity == NULL) {
> +		e = atomic_inc_return(&adev->mman.next_clear_entity) %
> +				      adev->mman.num_clear_entities;
> +		entity = &adev->mman.clear_entities[e];
> +	}
> +

Oh, that is really ugly.

I think you should have something like amdgpu_ttm_next_clear_entity() which returns the pointer round robin.

And then give that as parameter to amdgpu_fill_buffer().

Regards,
Christian.

>  	amdgpu_res_first(bo->tbo.resource, 0, amdgpu_bo_size(bo), &dst);
>  
>  	mutex_lock(&entity->gart_window_lock);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> index e8f8165f5bcf..781b0bdca56c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
> @@ -73,6 +73,7 @@ struct amdgpu_mman {
>  
>  	struct amdgpu_ttm_buffer_entity default_entity; /* has no gart windows */
>  	struct amdgpu_ttm_buffer_entity *clear_entities;
> +	atomic_t next_clear_entity;
>  	u32 num_clear_entities;
>  	struct amdgpu_ttm_buffer_entity move_entities[TTM_NUM_MOVE_FENCES];
>  	u32 num_move_entities;