Re: [PATCH v3 4/9] drm/scheduler: Add fence deadline support

[Rob Clark]

On Wed, Sep 22, 2021 at 7:31 AM Andrey Grodzovsky
<andrey.grodzovsky@xxxxxxx> wrote:
>
>
> On 2021-09-21 11:32 p.m., Rob Clark wrote:
> > On Tue, Sep 21, 2021 at 7:18 PM Andrey Grodzovsky
> > <andrey.grodzovsky@xxxxxxx> wrote:
> >>
> >> On 2021-09-21 4:47 p.m., Rob Clark wrote:
> >>> On Tue, Sep 21, 2021 at 1:09 PM Andrey Grodzovsky
> >>> <andrey.grodzovsky@xxxxxxx> wrote:
> >>>> On 2021-09-03 2:47 p.m., Rob Clark wrote:
> >>>>
> >>>>> From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >>>>>
> >>>>> 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.
> >>>>>
> >>>>> v2: Split into drm_sched_fence_set_parent() (ckoenig)
> >>>>>
> >>>>> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> >>>>> ---
> >>>>>     drivers/gpu/drm/scheduler/sched_fence.c | 34 +++++++++++++++++++++++++
> >>>>>     drivers/gpu/drm/scheduler/sched_main.c  |  2 +-
> >>>>>     include/drm/gpu_scheduler.h             |  8 ++++++
> >>>>>     3 files changed, 43 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c
> >>>>> index bcea035cf4c6..4fc41a71d1c7 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)
> >>>>> @@ -152,6 +177,15 @@ struct drm_sched_fence *to_drm_sched_fence(struct dma_fence *f)
> >>>>>     }
> >>>>>     EXPORT_SYMBOL(to_drm_sched_fence);
> >>>>>
> >>>>> +void drm_sched_fence_set_parent(struct drm_sched_fence *s_fence,
> >>>>> +                             struct dma_fence *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);
> >>>> I believe above you should pass be s_fence->finished to
> >>>> dma_fence_set_deadline
> >>>> instead it fence which is the HW fence itself.
> >>> Hmm, unless this has changed recently with some patches I don't have,
> >>> s_fence->parent is the one signalled by hw, so it is the one we want
> >>> to set the deadline on
> >>>
> >>> BR,
> >>> -R
> >>
> >> No it didn't change. But then when exactly will
> >> drm_sched_fence_set_deadline_finished
> >> execute such that fence->parent != NULL ? In other words, I am not clear
> >> how propagation
> >> happens otherwise - if dma_fence_set_deadline is called with the HW
> >> fence then the assumption
> >> here is that driver provided driver specific
> >> dma_fence_ops.dma_fence_set_deadline callback executes
> >> but I was under impression that drm_sched_fence_set_deadline_finished is
> >> the one that propagates
> >> the deadline to the HW fence's callback and for it to execute
> >> dma_fence_set_deadline needs to be called
> >> with s_fence->finished.
> > Assuming I didn't screw up drm/msm conversion to scheduler,
> > &s_fence->finished is the one that will be returned to userspace.. and
> > later passed back to kernel for atomic commit (or to the compositor).
> > So it is the one that fence->set_deadline() will be called on.  But
> > s_fence->parent is the actual hw fence that needs to know about the
> > deadline.  Depending on whether or not the job has been written into
> > hw ringbuffer or not, there are two cases:
> >
> > 1) not scheduled yet, s_fence will store the deadline and propagate it
> > later once s_fence->parent is known
>
>
> And by later you mean the call to drm_sched_fence_set_parent
> after HW fence is returned  ? If yes I think i get it now.

Yup :-)

BR,
-R

> Andrey
>
>
> > 2) already scheduled, in which case s_fence->finished.set_deadline
> > will propagate it directly to the real fence
> >
> > BR,
> > -R
> >
> >> Andrey
> >>
> >>
> >>
> >>>> Andrey
> >>>>
> >>>>
> >>>>> +}
> >>>>> +
> >>>>>     struct drm_sched_fence *drm_sched_fence_alloc(struct drm_sched_entity *entity,
> >>>>>                                               void *owner)
> >>>>>     {
> >>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> >>>>> index 595e47ff7d06..27bf0ac0625f 100644
> >>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
> >>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> >>>>> @@ -978,7 +978,7 @@ static int drm_sched_main(void *param)
> >>>>>                 drm_sched_fence_scheduled(s_fence);
> >>>>>
> >>>>>                 if (!IS_ERR_OR_NULL(fence)) {
> >>>>> -                     s_fence->parent = dma_fence_get(fence);
> >>>>> +                     drm_sched_fence_set_parent(s_fence, fence);
> >>>>>                         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 7f77a455722c..158ddd662469 100644
> >>>>> --- a/include/drm/gpu_scheduler.h
> >>>>> +++ b/include/drm/gpu_scheduler.h
> >>>>> @@ -238,6 +238,12 @@ 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
> >>>>> @@ -505,6 +511,8 @@ void drm_sched_entity_set_priority(struct drm_sched_entity *entity,
> >>>>>                                    enum drm_sched_priority priority);
> >>>>>     bool drm_sched_entity_is_ready(struct drm_sched_entity *entity);
> >>>>>
> >>>>> +void drm_sched_fence_set_parent(struct drm_sched_fence *s_fence,
> >>>>> +                             struct dma_fence *fence);
> >>>>>     struct drm_sched_fence *drm_sched_fence_alloc(
> >>>>>         struct drm_sched_entity *s_entity, void *owner);
> >>>>>     void drm_sched_fence_init(struct drm_sched_fence *fence,