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

[zhoucm1]

On 2018年08月02日 14:01, Nayan Deshmukh wrote:
> Hi David,
>
> On Thu, Aug 2, 2018 at 8:22 AM Zhou, David(ChunMing) 
> <David1.Zhou at amd.com <mailto: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.
Good handling I missed when reviewing them.

Cheers,
David Zhou
>
> 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
>     <mailto: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
>     <mailto:Andrey.Grodzovsky at amd.com>>
>     *Cc:* amd-gfx at lists.freedesktop.org
>     <mailto:amd-gfx at lists.freedesktop.org>; Maling list - DRI
>     developers <dri-devel at lists.freedesktop.org
>     <mailto:dri-devel at lists.freedesktop.org>>; Koenig, Christian
>     <Christian.Koenig at amd.com <mailto: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 <mailto: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
>         <mailto: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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