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

[Daniel Vetter <daniel@ffwll.ch>]

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?

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