[PATCH 2/2] drm/scheduler: add last_scheduled dependency handling

[Nayan Deshmukh]

Hi Christian,

Good patch. But it might lead to bad performance when we reschedule when
the hardware queue of the engine on which the last job was pushed is not
full.

On Mon, Aug 6, 2018 at 5:49 PM Christian König <
ckoenig.leichtzumerken at gmail.com> wrote:

> This fixes accessing the last_scheduled fence from multiple threads as
> well as makes it easier to move entities between schedulers.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  drivers/gpu/drm/scheduler/gpu_scheduler.c | 34
> +++++++++++++++++++++++++------
>  1 file changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> index 029863726c99..e4b71a543481 100644
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> @@ -523,6 +523,29 @@ static bool drm_sched_entity_add_dependency_cb(struct
> drm_sched_entity *entity)
>         return false;
>  }
>
> +static bool drm_sched_entity_last_scheduled_dep(struct drm_sched_entity
> *entity)
> +{
> +       struct drm_sched_fence *s_fence;
> +
> +       if (!entity->last_scheduled)
> +               return false;
> +
> +       /*
> +        * Check if the last submission was handled by a different
> scheduler
> +        */
> +       s_fence = to_drm_sched_fence(entity->last_scheduled);
> +       if (s_fence && s_fence->sched != entity->rq->sched) {
> +               entity->dependency = dma_fence_get(entity->last_scheduled);
> +               if (!dma_fence_add_callback(entity->dependency,
> &entity->cb,
> +                                           drm_sched_entity_wakeup))
> +                       return true;
> +
> +               dma_fence_put(entity->dependency);
> +               entity->dependency = NULL;
> +       }
> +       return false;
> +}
> +
>  static struct drm_sched_job *
>  drm_sched_entity_pop_job(struct drm_sched_entity *entity)
>  {
> @@ -537,6 +560,9 @@ drm_sched_entity_pop_job(struct drm_sched_entity
> *entity)
>                 if (drm_sched_entity_add_dependency_cb(entity))
>                         return NULL;
>
> +       if (drm_sched_entity_last_scheduled_dep(entity))
> +               return NULL;
> +
>         /* skip jobs from entity that marked guilty */
>         if (entity->guilty && atomic_read(entity->guilty))
>                 dma_fence_set_error(&sched_job->s_fence->finished,
> -ECANCELED);
> @@ -564,14 +590,10 @@ void drm_sched_entity_push_job(struct drm_sched_job
> *sched_job,
>                                struct drm_sched_entity *entity)
>  {
>         struct drm_sched_rq *rq = entity->rq;
> -       bool first, reschedule, idle;
> +       bool first;
>
> -       idle = entity->last_scheduled == NULL ||
> -               dma_fence_is_signaled(entity->last_scheduled);
>         first = spsc_queue_count(&entity->job_queue) == 0;
> -       reschedule = idle && first && (entity->num_rq_list > 1);
> -
> -       if (reschedule) {
> +       if (first && (entity->num_rq_list > 1)) {
>
Something like this might be better:

if (first  && (entity->num_rq_list > 1) &&
    (hw_rq_count == hw_submission_limit))

>                 rq = drm_sched_entity_get_free_sched(entity);
>                 spin_lock(&entity->rq_lock);
>                 drm_sched_rq_remove_entity(entity->rq, entity);
> --
> 2.14.1
>
> Regards,
Nayan
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