Re: [Linaro-mm-sig] Re: [PATCH 2/2] drm/msm: Embed the hw_fence in msm_gem_submit

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 13.03.23 um 17:43 schrieb Rob Clark:
> On Mon, Mar 13, 2023 at 9:15 AM Christian König
> <christian.koenig@xxxxxxx> wrote:
> > Am 13.03.23 um 15:45 schrieb Rob Clark:
> > > On Mon, Mar 13, 2023 at 12:19 AM Christian König
> > > <christian.koenig@xxxxxxx> wrote:
> > > > Am 11.03.23 um 18:35 schrieb Rob Clark:
> > > > > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> > > > >
> > > > > Avoid allocating memory in job_run() by embedding the fence in the
> > > > > submit object.  Since msm gpu fences are always 1:1 with msm_gem_submit
> > > > > we can just use the fence's refcnt to track the submit.  And since we
> > > > > can get the fence ctx from the submit we can just drop the msm_fence
> > > > > struct altogether.  This uses the new dma_fence_init_noref() to deal
> > > > > with the fact that the fence's refcnt is initialized when the submit is
> > > > > created, long before job_run().
> > > > Well this is a very very bad idea, we made the same mistake with amdgpu
> > > > as well.
> > > >
> > > > It's true that you should not have any memory allocation in your run_job
> > > > callback, but you could also just allocate the hw fence during job
> > > > creation and initializing it later on.
> > > >
> > > > I've suggested to embed the fence into the job for amdgpu because some
> > > > people insisted of re-submitting jobs during timeout and GPU reset. This
> > > > turned into a nightmare with tons of bug fixes on top of bug fixes on
> > > > top of bug fixes because it messes up the job and fence lifetime as
> > > > defined by the DRM scheduler and DMA-buf framework.
> > > >
> > > > Luben is currently working on cleaning all this up.
> > > This actually shouldn't be a problem with msm, as the fence doesn't
> > > change if there is a gpu reset.  We simply signal the fence for the
> > > offending job, reset the GPU, and re-play the remaining in-flight jobs
> > > (ie. things that already had their job_run() called) with the original
> > > fences.  (We don't use gpu sched's reset/timeout handling.. when I
> > > migrated to gpu sched I kept our existing hangcheck/recovery
> > > mechanism.)
> > That sounds much saner than what we did.
> >
> > So you basically need the dma_fence reference counting separate to
> > initializing the other dma_fence fields?
> yeah, that was the idea
>
> > What would happen if a dma_fence which is not completely initialized
> > gets freed? E.g. because of an error?
> hmm, yes, this would be a problem since ops->release is not set yet..
> and I'm relying on that to free the submit
>
> > Would it be to much to just keep the handling as it is today and only
> > allocate the dma_fence without initializing it? If necessary we could
> > easily add a dma_fence_is_initialized() function which checks the
> > fence_ops for NULL.
> Yeah, that would also be possible
>
> I guess we could split creation of the fence (initializing ops,
> refcount) and "arming" it later when the seqno is known?  But maybe
> that is going to too many lengths to avoid a separate allocation..

I would really like to avoid that. It give people the opportunity once 
more to do multiple "arm" operations on the same fence, and that was a 
really bad idea for us.

So yeah if that's just to avoid the extra allocation it's probably not 
worth it.

Christian.

> BR,
> -R
>
> > Thanks,
> > Christian.
> >
> > > BR,
> > > -R
> > >
> > > > Regards,
> > > > Christian.
> > > >
> > > > > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > > > > ---
> > > > > Note that this applies on top of https://patchwork.freedesktop.org/series/93035/
> > > > > out of convenience for myself, but I can re-work it to go before
> > > > > depending on the order that things land.
> > > > >
> > > > >     drivers/gpu/drm/msm/msm_fence.c      | 45 +++++++++++-----------------
> > > > >     drivers/gpu/drm/msm/msm_fence.h      |  2 +-
> > > > >     drivers/gpu/drm/msm/msm_gem.h        | 10 +++----
> > > > >     drivers/gpu/drm/msm/msm_gem_submit.c |  8 ++---
> > > > >     drivers/gpu/drm/msm/msm_gpu.c        |  4 +--
> > > > >     drivers/gpu/drm/msm/msm_ringbuffer.c |  4 +--
> > > > >     6 files changed, 31 insertions(+), 42 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c
> > > > > index 51b461f32103..51f9f1f0cb66 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_fence.c
> > > > > +++ b/drivers/gpu/drm/msm/msm_fence.c
> > > > > @@ -103,14 +103,9 @@ void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence)
> > > > >         spin_unlock_irqrestore(&fctx->spinlock, flags);
> > > > >     }
> > > > >
> > > > > -struct msm_fence {
> > > > > -     struct dma_fence base;
> > > > > -     struct msm_fence_context *fctx;
> > > > > -};
> > > > > -
> > > > > -static inline struct msm_fence *to_msm_fence(struct dma_fence *fence)
> > > > > +static inline struct msm_gem_submit *fence_to_submit(struct dma_fence *fence)
> > > > >     {
> > > > > -     return container_of(fence, struct msm_fence, base);
> > > > > +     return container_of(fence, struct msm_gem_submit, hw_fence);
> > > > >     }
> > > > >
> > > > >     static const char *msm_fence_get_driver_name(struct dma_fence *fence)
> > > > > @@ -120,20 +115,20 @@ static const char *msm_fence_get_driver_name(struct dma_fence *fence)
> > > > >
> > > > >     static const char *msm_fence_get_timeline_name(struct dma_fence *fence)
> > > > >     {
> > > > > -     struct msm_fence *f = to_msm_fence(fence);
> > > > > -     return f->fctx->name;
> > > > > +     struct msm_gem_submit *submit = fence_to_submit(fence);
> > > > > +     return submit->ring->fctx->name;
> > > > >     }
> > > > >
> > > > >     static bool msm_fence_signaled(struct dma_fence *fence)
> > > > >     {
> > > > > -     struct msm_fence *f = to_msm_fence(fence);
> > > > > -     return msm_fence_completed(f->fctx, f->base.seqno);
> > > > > +     struct msm_gem_submit *submit = fence_to_submit(fence);
> > > > > +     return msm_fence_completed(submit->ring->fctx, fence->seqno);
> > > > >     }
> > > > >
> > > > >     static void msm_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
> > > > >     {
> > > > > -     struct msm_fence *f = to_msm_fence(fence);
> > > > > -     struct msm_fence_context *fctx = f->fctx;
> > > > > +     struct msm_gem_submit *submit = fence_to_submit(fence);
> > > > > +     struct msm_fence_context *fctx = submit->ring->fctx;
> > > > >         unsigned long flags;
> > > > >         ktime_t now;
> > > > >
> > > > > @@ -165,26 +160,22 @@ static void msm_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
> > > > >         spin_unlock_irqrestore(&fctx->spinlock, flags);
> > > > >     }
> > > > >
> > > > > +static void msm_fence_release(struct dma_fence *fence)
> > > > > +{
> > > > > +     __msm_gem_submit_destroy(fence_to_submit(fence));
> > > > > +}
> > > > > +
> > > > >     static const struct dma_fence_ops msm_fence_ops = {
> > > > >         .get_driver_name = msm_fence_get_driver_name,
> > > > >         .get_timeline_name = msm_fence_get_timeline_name,
> > > > >         .signaled = msm_fence_signaled,
> > > > >         .set_deadline = msm_fence_set_deadline,
> > > > > +     .release = msm_fence_release,
> > > > >     };
> > > > >
> > > > > -struct dma_fence *
> > > > > -msm_fence_alloc(struct msm_fence_context *fctx)
> > > > > +void
> > > > > +msm_fence_init(struct msm_fence_context *fctx, struct dma_fence *f)
> > > > >     {
> > > > > -     struct msm_fence *f;
> > > > > -
> > > > > -     f = kzalloc(sizeof(*f), GFP_KERNEL);
> > > > > -     if (!f)
> > > > > -             return ERR_PTR(-ENOMEM);
> > > > > -
> > > > > -     f->fctx = fctx;
> > > > > -
> > > > > -     dma_fence_init(&f->base, &msm_fence_ops, &fctx->spinlock,
> > > > > -                    fctx->context, ++fctx->last_fence);
> > > > > -
> > > > > -     return &f->base;
> > > > > +     dma_fence_init_noref(f, &msm_fence_ops, &fctx->spinlock,
> > > > > +                          fctx->context, ++fctx->last_fence);
> > > > >     }
> > > > > diff --git a/drivers/gpu/drm/msm/msm_fence.h b/drivers/gpu/drm/msm/msm_fence.h
> > > > > index cdaebfb94f5c..8fca37e9773b 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_fence.h
> > > > > +++ b/drivers/gpu/drm/msm/msm_fence.h
> > > > > @@ -81,7 +81,7 @@ void msm_fence_context_free(struct msm_fence_context *fctx);
> > > > >     bool msm_fence_completed(struct msm_fence_context *fctx, uint32_t fence);
> > > > >     void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence);
> > > > >
> > > > > -struct dma_fence * msm_fence_alloc(struct msm_fence_context *fctx);
> > > > > +void msm_fence_init(struct msm_fence_context *fctx, struct dma_fence *f);
> > > > >
> > > > >     static inline bool
> > > > >     fence_before(uint32_t a, uint32_t b)
> > > > > diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> > > > > index c4844cf3a585..e06afed99d5b 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_gem.h
> > > > > +++ b/drivers/gpu/drm/msm/msm_gem.h
> > > > > @@ -259,10 +259,10 @@ struct msm_gem_submit {
> > > > >         struct ww_acquire_ctx ticket;
> > > > >         uint32_t seqno;         /* Sequence number of the submit on the ring */
> > > > >
> > > > > -     /* Hw fence, which is created when the scheduler executes the job, and
> > > > > +     /* Hw fence, which is initialized when the scheduler executes the job, and
> > > > >          * is signaled when the hw finishes (via seqno write from cmdstream)
> > > > >          */
> > > > > -     struct dma_fence *hw_fence;
> > > > > +     struct dma_fence hw_fence;
> > > > >
> > > > >         /* Userspace visible fence, which is signaled by the scheduler after
> > > > >          * the hw_fence is signaled.
> > > > > @@ -309,16 +309,16 @@ static inline struct msm_gem_submit *to_msm_submit(struct drm_sched_job *job)
> > > > >         return container_of(job, struct msm_gem_submit, base);
> > > > >     }
> > > > >
> > > > > -void __msm_gem_submit_destroy(struct kref *kref);
> > > > > +void __msm_gem_submit_destroy(struct msm_gem_submit *submit);
> > > > >
> > > > >     static inline void msm_gem_submit_get(struct msm_gem_submit *submit)
> > > > >     {
> > > > > -     kref_get(&submit->ref);
> > > > > +     dma_fence_get(&submit->hw_fence);
> > > > >     }
> > > > >
> > > > >     static inline void msm_gem_submit_put(struct msm_gem_submit *submit)
> > > > >     {
> > > > > -     kref_put(&submit->ref, __msm_gem_submit_destroy);
> > > > > +     dma_fence_put(&submit->hw_fence);
> > > > >     }
> > > > >
> > > > >     void msm_submit_retire(struct msm_gem_submit *submit);
> > > > > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > > > > index be4bf77103cd..522c8c82e827 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > > > > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > > > > @@ -47,7 +47,7 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
> > > > >                 return ERR_PTR(ret);
> > > > >         }
> > > > >
> > > > > -     kref_init(&submit->ref);
> > > > > +     kref_init(&submit->hw_fence.refcount);
> > > > >         submit->dev = dev;
> > > > >         submit->aspace = queue->ctx->aspace;
> > > > >         submit->gpu = gpu;
> > > > > @@ -65,10 +65,9 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
> > > > >         return submit;
> > > > >     }
> > > > >
> > > > > -void __msm_gem_submit_destroy(struct kref *kref)
> > > > > +/* Called when the hw_fence is destroyed: */
> > > > > +void __msm_gem_submit_destroy(struct msm_gem_submit *submit)
> > > > >     {
> > > > > -     struct msm_gem_submit *submit =
> > > > > -                     container_of(kref, struct msm_gem_submit, ref);
> > > > >         unsigned i;
> > > > >
> > > > >         if (submit->fence_id) {
> > > > > @@ -78,7 +77,6 @@ void __msm_gem_submit_destroy(struct kref *kref)
> > > > >         }
> > > > >
> > > > >         dma_fence_put(submit->user_fence);
> > > > > -     dma_fence_put(submit->hw_fence);
> > > > >
> > > > >         put_pid(submit->pid);
> > > > >         msm_submitqueue_put(submit->queue);
> > > > > diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> > > > > index 380249500325..a82d11dd5fcf 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_gpu.c
> > > > > +++ b/drivers/gpu/drm/msm/msm_gpu.c
> > > > > @@ -716,7 +716,7 @@ static void retire_submits(struct msm_gpu *gpu)
> > > > >                          * been signalled, then later submits are not signalled
> > > > >                          * either, so we are also done.
> > > > >                          */
> > > > > -                     if (submit && dma_fence_is_signaled(submit->hw_fence)) {
> > > > > +                     if (submit && dma_fence_is_signaled(&submit->hw_fence)) {
> > > > >                                 retire_submit(gpu, ring, submit);
> > > > >                         } else {
> > > > >                                 break;
> > > > > @@ -760,7 +760,7 @@ void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
> > > > >
> > > > >         msm_gpu_hw_init(gpu);
> > > > >
> > > > > -     submit->seqno = submit->hw_fence->seqno;
> > > > > +     submit->seqno = submit->hw_fence.seqno;
> > > > >
> > > > >         msm_rd_dump_submit(priv->rd, submit, NULL);
> > > > >
> > > > > diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
> > > > > index 57a8e9564540..5c54befa2427 100644
> > > > > --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
> > > > > +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
> > > > > @@ -18,7 +18,7 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
> > > > >         struct msm_gpu *gpu = submit->gpu;
> > > > >         int i;
> > > > >
> > > > > -     submit->hw_fence = msm_fence_alloc(fctx);
> > > > > +     msm_fence_init(fctx, &submit->hw_fence);
> > > > >
> > > > >         for (i = 0; i < submit->nr_bos; i++) {
> > > > >                 struct drm_gem_object *obj = &submit->bos[i].obj->base;
> > > > > @@ -37,7 +37,7 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
> > > > >
> > > > >         mutex_unlock(&gpu->lock);
> > > > >
> > > > > -     return dma_fence_get(submit->hw_fence);
> > > > > +     return dma_fence_get(&submit->hw_fence);
> > > > >     }
> > > > >
> > > > >     static void msm_job_free(struct drm_sched_job *job)
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