[PATCH 1/2] drm/scheduler: bind job earlier to scheduler

[Christian König]

Am 06.08.2018 um 15:11 schrieb Nayan Deshmukh:
> Hi Christian,
>
> On Mon, Aug 6, 2018 at 5:49 PM Christian König 
> <ckoenig.leichtzumerken at gmail.com 
> <mailto:ckoenig.leichtzumerken at gmail.com>> wrote:
>
>     Update job earlier with the scheduler it is supposed to be
>     scheduled on.
>
>     Otherwise we could incorrectly optimize dependencies when moving an
>     entity from one scheduler to another.
>
> I don't think change is really required, the old code should work 
> fine. Read below for more comments.
>
>
>     Signed-off-by: Christian König <christian.koenig at amd.com
>     <mailto:christian.koenig at amd.com>>
>     ---
>      drivers/gpu/drm/scheduler/gpu_scheduler.c | 4 ++--
>      drivers/gpu/drm/scheduler/sched_fence.c   | 2 +-
>      2 files changed, 3 insertions(+), 3 deletions(-)
>
>     diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
>     b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>     index 65078dd3c82c..029863726c99 100644
>     --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
>     +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>     @@ -533,8 +533,6 @@ drm_sched_entity_pop_job(struct
>     drm_sched_entity *entity)
>             if (!sched_job)
>                     return NULL;
>
>     -       sched_job->sched = sched;
>     -       sched_job->s_fence->sched = sched;
>             while ((entity->dependency =
>     sched->ops->dependency(sched_job, entity)))
>
> The job should have the correct scheduler before the 
> sched->oops->dependency() function is called for the first time. Hence 
> I placed the assignment here.
>
> It might also be that I am missing some case so please let me know if 
> such a case exists where this might lead to wrong optimization.

The problem is that the scheduler fence of job A could be the dependency 
of another job B

Job B then makes an incorrect optimization because it sees the wrong 
scheduler in the scheduler fence of job A.

Regards,
Christian.

>
> Regards,
> Nayan
>
>                     if (drm_sched_entity_add_dependency_cb(entity))
>                             return NULL;
>     @@ -581,6 +579,8 @@ void drm_sched_entity_push_job(struct
>     drm_sched_job *sched_job,
>                     spin_unlock(&entity->rq_lock);
>             }
>
>     +       sched_job->sched = entity->rq->sched;
>     +       sched_job->s_fence->sched = entity->rq->sched;
>             trace_drm_sched_job(sched_job, entity);
>     atomic_inc(&entity->rq->sched->num_jobs);
>             WRITE_ONCE(entity->last_user, current->group_leader);
>     diff --git a/drivers/gpu/drm/scheduler/sched_fence.c
>     b/drivers/gpu/drm/scheduler/sched_fence.c
>     index 4029312fdd81..6dab18d288d7 100644
>     --- a/drivers/gpu/drm/scheduler/sched_fence.c
>     +++ b/drivers/gpu/drm/scheduler/sched_fence.c
>     @@ -172,7 +172,7 @@ struct drm_sched_fence
>     *drm_sched_fence_create(struct drm_sched_entity *entity,
>                     return NULL;
>
>             fence->owner = owner;
>     -       fence->sched = entity->rq->sched;
>     +       fence->sched = NULL;
>             spin_lock_init(&fence->lock);
>
>             seq = atomic_inc_return(&entity->fence_seq);
>     -- 
>     2.14.1
>

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