[PATCH 3/4] drm/scheduler: add new function to get least loaded sched v2

[Nayan Deshmukh]

Hi David,

On Thu, Aug 2, 2018 at 8:22 AM Zhou, David(ChunMing) <David1.Zhou at amd.com>
wrote:

> Another big question:
>
> I agree the general idea is good to balance scheduler load for same ring
> family.
>
> But, when same entity job run on different scheduler, that means the later
> job could be completed ahead of front, Right?
>
Really good question. To avoid this senario we do not move an entity which
already has a job in the hardware queue. We only move entities whose
last_scheduled fence has been signalled which means that the last submitted
job of this entity has finished executing.

Moving an entity which already has a job in the hardware queue will hinder
the dependency optimization that we are using and hence will not anyway
lead to a better performance. I have talked about the issue in more detail
here [1]. Please let me know if you have any more doubts regarding this.

Cheers,
Nayan

[1]
http://ndesh26.github.io/gsoc/2018/06/14/GSoC-Update-A-Curious-Case-of-Dependency-Handling/

That will break fence design, later fence must be signaled after front
> fence in same fence context.
>
>
>
> Anything I missed?
>
>
>
> Regards,
>
> David Zhou
>
>
>
> *From:* dri-devel <dri-devel-bounces at lists.freedesktop.org> *On Behalf Of
> *Nayan Deshmukh
> *Sent:* Thursday, August 02, 2018 12:07 AM
> *To:* Grodzovsky, Andrey <Andrey.Grodzovsky at amd.com>
> *Cc:* amd-gfx at lists.freedesktop.org; Maling list - DRI developers <
> dri-devel at lists.freedesktop.org>; Koenig, Christian <
> Christian.Koenig at amd.com>
> *Subject:* Re: [PATCH 3/4] drm/scheduler: add new function to get least
> loaded sched v2
>
>
>
> Yes, that is correct.
>
>
>
> Nayan
>
>
>
> On Wed, Aug 1, 2018, 9:05 PM Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
> wrote:
>
> Clarification question -  if the run queues belong to different
> schedulers they effectively point to different rings,
>
> it means we allow to move (reschedule) a drm_sched_entity from one ring
> to another - i assume that the idea int the first place, that
>
> you have a set of HW rings and you can utilize any of them for your jobs
> (like compute rings). Correct ?
>
> Andrey
>
>
> On 08/01/2018 04:20 AM, Nayan Deshmukh wrote:
> > 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.
> >
> > v2: avoid using atomic read twice consecutively, instead store
> >      it locally
> >
> > Signed-off-by: Nayan Deshmukh <nayan26deshmukh at gmail.com>
> > ---
> >   drivers/gpu/drm/scheduler/gpu_scheduler.c | 25
> +++++++++++++++++++++++++
> >   1 file changed, 25 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > index 375f6f7f6a93..fb4e542660b0 100644
> > --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > @@ -255,6 +255,31 @@ 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, num_jobs;
> > +     int i;
> > +
> > +     for (i = 0; i < entity->num_rq_list; ++i) {
> > +             num_jobs =
> atomic_read(&entity->rq_list[i]->sched->num_jobs);
> > +             if (num_jobs < min_jobs) {
> > +                     min_jobs = num_jobs;
> > +                     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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