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Message-ID: <YTj2scNdCHAdF+cl@phenom.ffwll.local>
Date: Wed, 8 Sep 2021 19:45:21 +0200
From: Daniel Vetter <daniel@...ll.ch>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
Daniel Vetter <daniel@...ll.ch>,
Christian König
<ckoenig.leichtzumerken@...il.com>,
Michel Dänzer <michel@...nzer.net>,
Pekka Paalanen <ppaalanen@...il.com>,
Rob Clark <robdclark@...omium.org>,
David Airlie <airlied@...ux.ie>,
Sumit Semwal <sumit.semwal@...aro.org>,
Christian König <christian.koenig@....com>,
Tian Tao <tiantao6@...ilicon.com>,
Steven Price <steven.price@....com>,
Melissa Wen <mwen@...lia.com>,
Luben Tuikov <luben.tuikov@....com>,
Andrey Grodzovsky <andrey.grodzovsky@....com>,
Boris Brezillon <boris.brezillon@...labora.com>,
Jack Zhang <Jack.Zhang1@....com>,
open list <linux-kernel@...r.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@...r.kernel.org>
Subject: Re: [PATCH v3 4/9] drm/scheduler: Add fence deadline support
On Fri, Sep 03, 2021 at 11:47:55AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.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.
>
> v2: Split into drm_sched_fence_set_parent() (ckoenig)
>
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
> 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))
Don't you need the spinlock here too to avoid races? test_bit is very
unordered, so guarantees nothing. Spinlock would need to be both around
->parent = and the test_bit.
Entirely aside, but there's discussions going on to preallocate the hw
fence somehow. If we do that we could make the deadline forwarding
lockless here. Having a spinlock just to set the parent is a bit annoying
...
Alternative is that you do this locklessly with barriers and a _lot_ of
comments. Would be good to benchmark whether the overhead matters though
first.
-Daniel
> + dma_fence_set_deadline(fence, s_fence->deadline);
> +}
> +
> 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,
> --
> 2.31.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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