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

On Mon, Aug 16, 2021 at 8:38 AM Daniel Vetter [off-list ref] wrote:

On Mon, Aug 16, 2021 at 12:14:35PM +0200, Christian König wrote:

quoted

Am 07.08.21 um 20:37 schrieb Rob Clark:

quoted

From: Rob Clark <redacted>

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 <redacted>

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

quoted

quoted

---
  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.

quoted

                    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