Re: [Intel-xe] [PATCH] drm/sched: Eliminate drm_sched_run_job_queue_if_ready()

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Nov 02, 2023 at 06:46:54PM -0400, Luben Tuikov wrote:
> Eliminate drm_sched_run_job_queue_if_ready() and instead just call
> drm_sched_run_job_queue() in drm_sched_free_job_work(). The problem is that
> the former function uses drm_sched_select_entity() to determine if the
> scheduler had an entity ready in one of its run-queues, and in the case of the
> Round-Robin (RR) scheduling, the function drm_sched_rq_select_entity_rr() does
> just that, selects the _next_ entity which is ready, sets up the run-queue and
> completion and returns that entity. The FIFO scheduling algorithm is unaffected.
> 
> Now, since drm_sched_run_job_work() also calls drm_sched_select_entity(), then
> in the case of RR scheduling, that would result in calling select_entity()
> twice, which may result in skipping a ready entity if more than one entity is
> ready. This commit fixes this by eliminating the if_ready() variant.
> 

Ah, yes I guess we both missed this. What about reviving the peek
argument [1]? This would avoid unnecessary re-queues. 

Matt

[1] https://patchwork.freedesktop.org/patch/562222/?series=121744&rev=7

> Signed-off-by: Luben Tuikov <ltuikov89@gmail.com>
> ---
>  drivers/gpu/drm/scheduler/sched_main.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 98b2ad54fc7071..05816e7cae8c8b 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -1040,16 +1040,6 @@ drm_sched_pick_best(struct drm_gpu_scheduler **sched_list,
>  }
>  EXPORT_SYMBOL(drm_sched_pick_best);
>  
> -/**
> - * drm_sched_run_job_queue_if_ready - enqueue run-job work if ready
> - * @sched: scheduler instance
> - */
> -static void drm_sched_run_job_queue_if_ready(struct drm_gpu_scheduler *sched)
> -{
> -	if (drm_sched_select_entity(sched))
> -		drm_sched_run_job_queue(sched);
> -}
> -
>  /**
>   * drm_sched_free_job_work - worker to call free_job
>   *
> @@ -1069,7 +1059,7 @@ static void drm_sched_free_job_work(struct work_struct *w)
>  		sched->ops->free_job(cleanup_job);
>  
>  		drm_sched_free_job_queue_if_done(sched);
> -		drm_sched_run_job_queue_if_ready(sched);
> +		drm_sched_run_job_queue(sched);
>  	}
>  }
>  
> @@ -1127,7 +1117,7 @@ static void drm_sched_run_job_work(struct work_struct *w)
>  	}
>  
>  	wake_up(&sched->job_scheduled);
> -	drm_sched_run_job_queue_if_ready(sched);
> +	drm_sched_run_job_queue(sched);
>  }
>  
>  /**
> 
> base-commit: 6fd9487147c4f18ad77eea00bd8c9189eec74a3e
> -- 
> 2.42.1
>