linux-kernel - Re: [PATCH v4 2/3] drm/amdgpu: increment sched score on entity selection

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Message-ID: <5717c024-0200-4b23-a25b-681ef0937d6f@amd.com>
Date: Fri, 7 Nov 2025 11:26:29 +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: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] drm/amdgpu: increment sched score on entity
 selection



On 11/7/25 10:04, Pierre-Eric Pelloux-Prayer wrote:
> For hw engines that can't load balance jobs, entities are
> "statically" load balanced: on their first submit, they select
> the best scheduler based on its score.
> The score is made up of 2 parts:
> * the job queue depth (how much jobs are executing/waiting)
> * the number of entities assigned
> 
> The second part is only relevant for the static load balance:
> it's a way to consider how many entities are attached to this
> scheduler, knowing that if they ever submit jobs they will go
> to this one.
> 
> For rings that can load balance jobs freely, idle entities
> aren't a concern and shouldn't impact the scheduler's decisions.
> 
> Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 22 +++++++++++++++++-----
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h |  1 +
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> index afedea02188d..4d91cbcbcf25 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c
> @@ -209,6 +209,7 @@ static int amdgpu_ctx_init_entity(struct amdgpu_ctx *ctx, u32 hw_ip,
>  	struct amdgpu_ctx_entity *entity;
>  	enum drm_sched_priority drm_prio;
>  	unsigned int hw_prio, num_scheds;
> +	struct amdgpu_ring *aring;
>  	int32_t ctx_prio;
>  	int r;
>  
> @@ -239,11 +240,13 @@ static int amdgpu_ctx_init_entity(struct amdgpu_ctx *ctx, u32 hw_ip,
>  			goto error_free_entity;
>  	}
>  
> -	/* disable load balance if the hw engine retains context among dependent jobs */
> -	if (hw_ip == AMDGPU_HW_IP_VCN_ENC ||
> -	    hw_ip == AMDGPU_HW_IP_VCN_DEC ||
> -	    hw_ip == AMDGPU_HW_IP_UVD_ENC ||
> -	    hw_ip == AMDGPU_HW_IP_UVD) {
> +	sched = scheds[0];
> +	aring = container_of(sched, struct amdgpu_ring, sched);
> +
> +	if (aring->funcs->engine_retains_context) {
> +		/* Disable load balancing between multiple schedulers if the hw
> +		 * engine retains context among dependent jobs.
> +		 */
>  		sched = drm_sched_pick_best(scheds, num_scheds);
>  		scheds = &sched;
>  		num_scheds = 1;
> @@ -258,6 +261,12 @@ static int amdgpu_ctx_init_entity(struct amdgpu_ctx *ctx, u32 hw_ip,
>  	if (cmpxchg(&ctx->entities[hw_ip][ring], NULL, entity))
>  		goto cleanup_entity;
>  
> +	if (aring->funcs->engine_retains_context) {
> +		aring = container_of(sched, struct amdgpu_ring, sched);
> +		entity->sched_score = aring->sched_score;
> +		atomic_inc(entity->sched_score);
> +	}
> +
>  	return 0;
>  
>  cleanup_entity:
> @@ -514,6 +523,9 @@ static void amdgpu_ctx_do_release(struct kref *ref)
>  			if (!ctx->entities[i][j])
>  				continue;
>  
> +			if (ctx->entities[i][j]->sched_score)
> +				atomic_dec(ctx->entities[i][j]->sched_score);
> +
>  			drm_sched_entity_destroy(&ctx->entities[i][j]->entity);
>  		}
>  	}
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> index 090dfe86f75b..f7b44f96f374 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.h
> @@ -39,6 +39,7 @@ struct amdgpu_ctx_entity {
>  	uint32_t		hw_ip;
>  	uint64_t		sequence;
>  	struct drm_sched_entity	entity;
> +	atomic_t		*sched_score;

I would rather prefer to not have that additional member here.

Additional to that we are messing with the internals of the scheduler here and should probably have two clean functions to increase/decrease the score.

Regards,
Christian.

>  	struct dma_fence	*fences[];
>  };
>