Re: [PATCH 3/4] drm/scheduler: add new function to get least loaded sched

[Nayan Deshmukh <nayan26deshmukh-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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I will take care of that in v2.

On Tue, Jul 31, 2018 at 4:57 PM Christian König <
ckoenig.leichtzumerken-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> Am 31.07.2018 um 12:37 schrieb Nayan Deshmukh:
> > The function selects the run queue from the rq_list with the
> > least load. The load is decided by the number of jobs in a
> > scheduler.
> >
> > Signed-off-by: Nayan Deshmukh <nayan26deshmukh-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > ---
> >   drivers/gpu/drm/scheduler/gpu_scheduler.c | 26
> ++++++++++++++++++++++++++
> >   1 file changed, 26 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > index 375f6f7f6a93..c67f65ad8f15 100644
> > --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > @@ -255,6 +255,32 @@ static bool drm_sched_entity_is_ready(struct
> drm_sched_entity *entity)
> >       return true;
> >   }
> >
> > +/**
> > + * drm_sched_entity_get_free_sched - Get the rq from rq_list with least
> load
> > + *
> > + * @entity: scheduler entity
> > + *
> > + * Return the pointer to the rq with least load.
> > + */
> > +static struct drm_sched_rq *
> > +drm_sched_entity_get_free_sched(struct drm_sched_entity *entity)
> > +{
> > +     struct drm_sched_rq *rq = NULL;
> > +     unsigned int min_jobs = UINT_MAX;
> > +     int i;
> > +
> > +     for (i = 0; i < entity->num_rq_list; ++i) {
> > +             if (atomic_read(&entity->rq_list[i]->sched->num_jobs) <
> > +                             min_jobs) {
> > +                     min_jobs = atomic_read(
> > +
>  &entity->rq_list[i]->sched->num_jobs);
>
> When you use atomic_read twice you might get different results because
> the atomic has changed in the meantime.
>
> In other words you need to store the result locally:
>
> unsigned int num_jobs = atomic_read(....);
>
> if (num_jobs < min_jobs) {
>      min_jobs = num_jobs;
>      .....
>
> Christian.
>
> > +                     rq = entity->rq_list[i];
> > +             }
> > +     }
> > +
> > +     return rq;
> > +}
> > +
> >   static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
> >                                   struct dma_fence_cb *cb)
> >   {
>
>

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