Re: [PATCH 2/2] drm/scheduler: stop setting rq to NULL

[Andrey Grodzovsky <Andrey.Grodzovsky@xxxxxxx>]

Thinking again about this change and 53d5f1e drm/scheduler: move idle 
entities to scheduler with less load v2

Looks to me like use case for which fc9a539 drm/scheduler: add NULL 
pointer check for run queue (v2) was done

will not work anymore.

First of all in drm_sched_entity_push_job, 'if (!entity->rq)' will never 
be true any more since we stopped entity->rq to NULL in

drm_sched_entity_flush.

Second of all, even after we removed the entity from rq in 
drm_sched_entity_flush to terminate any subsequent submissions

to the queue the other thread doing push job can just acquire again a 
run queue

from drm_sched_entity_get_free_sched and continue submission so you 
can't substitute ' if (!entity->rq)' to 'if (list_empty(&entity->list))'.

What about adding a 'stopped' flag to drm_sched_entity to be set in 
drm_sched_entity_flush and in

drm_sched_entity_push_job check for  'if (!entity->stopped)' instead of  
' if (!entity->rq)' ?

Andrey


On 07/30/2018 07:03 AM, Christian König wrote:
> We removed the redundancy of having an extra scheduler field, so we
> can't set the rq to NULL any more or otherwise won't know which
> scheduler to use for the cleanup.
>
> Just remove the entity from the scheduling list instead.
>
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> ---
>   drivers/gpu/drm/scheduler/gpu_scheduler.c | 35 +++++++------------------------
>   1 file changed, 8 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> index f563e4fbb4b6..1b733229201e 100644
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> @@ -198,21 +198,6 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
>   }
>   EXPORT_SYMBOL(drm_sched_entity_init);
>   
> -/**
> - * drm_sched_entity_is_initialized - Query if entity is initialized
> - *
> - * @sched: Pointer to scheduler instance
> - * @entity: The pointer to a valid scheduler entity
> - *
> - * return true if entity is initialized, false otherwise
> -*/
> -static bool drm_sched_entity_is_initialized(struct drm_gpu_scheduler *sched,
> -					    struct drm_sched_entity *entity)
> -{
> -	return entity->rq != NULL &&
> -		entity->rq->sched == sched;
> -}
> -
>   /**
>    * drm_sched_entity_is_idle - Check if entity is idle
>    *
> @@ -224,7 +209,8 @@ static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)
>   {
>   	rmb();
>   
> -	if (!entity->rq || spsc_queue_peek(&entity->job_queue) == NULL)
> +	if (list_empty(&entity->list) ||
> +	    spsc_queue_peek(&entity->job_queue) == NULL)
>   		return true;
>   
>   	return false;
> @@ -279,8 +265,6 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
>   	long ret = timeout;
>   
>   	sched = entity->rq->sched;
> -	if (!drm_sched_entity_is_initialized(sched, entity))
> -		return ret;
>   	/**
>   	 * The client will not queue more IBs during this fini, consume existing
>   	 * queued IBs or discard them on SIGKILL
> @@ -299,7 +283,7 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
>   	last_user = cmpxchg(&entity->last_user, current->group_leader, NULL);
>   	if ((!last_user || last_user == current->group_leader) &&
>   	    (current->flags & PF_EXITING) && (current->exit_code == SIGKILL))
> -		drm_sched_entity_set_rq(entity, NULL);
> +		drm_sched_rq_remove_entity(entity->rq, entity);
>   
>   	return ret;
>   }
> @@ -320,7 +304,7 @@ void drm_sched_entity_fini(struct drm_sched_entity *entity)
>   	struct drm_gpu_scheduler *sched;
>   
>   	sched = entity->rq->sched;
> -	drm_sched_entity_set_rq(entity, NULL);
> +	drm_sched_rq_remove_entity(entity->rq, entity);
>   
>   	/* Consumption of existing IBs wasn't completed. Forcefully
>   	 * remove them here.
> @@ -416,15 +400,12 @@ void drm_sched_entity_set_rq(struct drm_sched_entity *entity,
>   	if (entity->rq == rq)
>   		return;
>   
> -	spin_lock(&entity->rq_lock);
> -
> -	if (entity->rq)
> -		drm_sched_rq_remove_entity(entity->rq, entity);
> +	BUG_ON(!rq);
>   
> +	spin_lock(&entity->rq_lock);
> +	drm_sched_rq_remove_entity(entity->rq, entity);
>   	entity->rq = rq;
> -	if (rq)
> -		drm_sched_rq_add_entity(rq, entity);
> -
> +	drm_sched_rq_add_entity(rq, entity);
>   	spin_unlock(&entity->rq_lock);
>   }
>   EXPORT_SYMBOL(drm_sched_entity_set_rq);

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