Re: [PATCH v2 4/5] drm/scheduler: Add fence deadline support

[Rob Clark <robdclark@gmail.com>]

On Mon, Aug 16, 2021 at 8:38 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> On Mon, Aug 16, 2021 at 12:14:35PM +0200, Christian König wrote:
> > Am 07.08.21 um 20:37 schrieb Rob Clark:
> > > From: Rob Clark <robdclark@chromium.org>
> > >
> > > As the finished fence is the one that is exposed to userspace, and
> > > therefore the one that other operations, like atomic update, would
> > > block on, we need to propagate the deadline from from the finished
> > > fence to the actual hw fence.
> > >
> > > Signed-off-by: Rob Clark <robdclark@chromium.org>
>
> I guess you're already letting the compositor run at a higher gpu priority
> so that your deadline'd drm_sched_job isn't stuck behind the app rendering
> the next frame?

With the scheduler conversion we do have multiple priorities (provided
by scheduler) for all generations.. but not yet preemption for all
generations.

But the most common use-case where we need this ends up being display
composition (either fullscreen app/game or foreground app/game
composited via overlay) so I haven't thought too much about the next
step of boosting job priority.  I might leave that to someone who
already has preemption wired up ;-)

BR,
-R

> I'm not sure whether you wire that one up as part of the conversion to
> drm/sched. Without that I think we might need to ponder how we can do a
> prio-boost for these, e.g. within a scheduling class we pick the jobs with
> the nearest deadline first, before we pick others.
> -Daniel
>
> > > ---
> > >   drivers/gpu/drm/scheduler/sched_fence.c | 25 +++++++++++++++++++++++++
> > >   drivers/gpu/drm/scheduler/sched_main.c  |  3 +++
> > >   include/drm/gpu_scheduler.h             |  6 ++++++
> > >   3 files changed, 34 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
> > > index 69de2c76731f..f389dca44185 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_fence.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_fence.c
> > > @@ -128,6 +128,30 @@ static void drm_sched_fence_release_finished(struct dma_fence *f)
> > >     dma_fence_put(&fence->scheduled);
> > >   }
> > > +static void drm_sched_fence_set_deadline_finished(struct dma_fence *f,
> > > +                                             ktime_t deadline)
> > > +{
> > > +   struct drm_sched_fence *fence = to_drm_sched_fence(f);
> > > +   unsigned long flags;
> > > +
> > > +   spin_lock_irqsave(&fence->lock, flags);
> > > +
> > > +   /* If we already have an earlier deadline, keep it: */
> > > +   if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &f->flags) &&
> > > +       ktime_before(fence->deadline, deadline)) {
> > > +           spin_unlock_irqrestore(&fence->lock, flags);
> > > +           return;
> > > +   }
> > > +
> > > +   fence->deadline = deadline;
> > > +   set_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &f->flags);
> > > +
> > > +   spin_unlock_irqrestore(&fence->lock, flags);
> > > +
> > > +   if (fence->parent)
> > > +           dma_fence_set_deadline(fence->parent, deadline);
> > > +}
> > > +
> > >   static const struct dma_fence_ops drm_sched_fence_ops_scheduled = {
> > >     .get_driver_name = drm_sched_fence_get_driver_name,
> > >     .get_timeline_name = drm_sched_fence_get_timeline_name,
> > > @@ -138,6 +162,7 @@ static const struct dma_fence_ops drm_sched_fence_ops_finished = {
> > >     .get_driver_name = drm_sched_fence_get_driver_name,
> > >     .get_timeline_name = drm_sched_fence_get_timeline_name,
> > >     .release = drm_sched_fence_release_finished,
> > > +   .set_deadline = drm_sched_fence_set_deadline_finished,
> > >   };
> > >   struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f)
> > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > > index a2a953693b45..3ab0900d3596 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > @@ -818,6 +818,9 @@ static int drm_sched_main(void *param)
> > >             if (!IS_ERR_OR_NULL(fence)) {
> > >                     s_fence->parent = dma_fence_get(fence);
> > > +                   if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
> > > +                                &s_fence->finished.flags))
> > > +                           dma_fence_set_deadline(fence, s_fence->deadline);
> >
> > Maybe move this into a dma_sched_fence_set_parent() function.
> >
> > Apart from that looks good to me.
> >
> > Regards,
> > Christian.
> >
> > >                     r = dma_fence_add_callback(fence, &sched_job->cb,
> > >                                                drm_sched_job_done_cb);
> > >                     if (r == -ENOENT)
> > > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > > index d18af49fd009..0f08ade614ae 100644
> > > --- a/include/drm/gpu_scheduler.h
> > > +++ b/include/drm/gpu_scheduler.h
> > > @@ -144,6 +144,12 @@ struct drm_sched_fence {
> > >            */
> > >     struct dma_fence                finished;
> > > +   /**
> > > +    * @deadline: deadline set on &drm_sched_fence.finished which
> > > +    * potentially needs to be propagated to &drm_sched_fence.parent
> > > +    */
> > > +   ktime_t                         deadline;
> > > +
> > >           /**
> > >            * @parent: the fence returned by &drm_sched_backend_ops.run_job
> > >            * when scheduling the job on hardware. We signal the
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch