linux-kernel - Re: [PATCH v2 0/5] dma-fence: Deadline awareness

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Date:   Mon, 16 Aug 2021 15:29:49 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Rob Clark <robdclark@...omium.org>,
        Alex Deucher <alexander.deucher@....com>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Jack Zhang <Jack.Zhang1@....com>,
        Lee Jones <lee.jones@...aro.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>, Luben Tuikov <luben.tuikov@....com>,
        Steven Price <steven.price@....com>,
        Tian Tao <tiantao6@...ilicon.com>
Subject: Re: [PATCH v2 0/5] dma-fence: Deadline awareness

dma_fence_array looks simple enough, just propagate the deadline to
all children.

I guess dma_fence_chain is similar (ie. fence is signalled when all
children are signalled), the difference being simply that children are
added dynamically?

BR,
-R

On Mon, Aug 16, 2021 at 3:17 AM Christian König
<christian.koenig@....com> wrote:
>
> The general approach seems to make sense now I think.
>
> One minor thing which I'm missing is adding support for this to the
> dma_fence_array and dma_fence_chain containers.
>
> Regards,
> Christian.
>
> Am 07.08.21 um 20:37 schrieb Rob Clark:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Based on discussion from a previous series[1] to add a "boost" mechanism
> > when, for example, vblank deadlines are missed.  Instead of a boost
> > callback, this approach adds a way to set a deadline on the fence, by
> > which the waiter would like to see the fence signalled.
> >
> > I've not yet had a chance to re-work the drm/msm part of this, but
> > wanted to send this out as an RFC in case I don't have a chance to
> > finish the drm/msm part this week.
> >
> > Original description:
> >
> > In some cases, like double-buffered rendering, missing vblanks can
> > trick the GPU into running at a lower frequence, when really we
> > want to be running at a higher frequency to not miss the vblanks
> > in the first place.
> >
> > This is partially inspired by a trick i915 does, but implemented
> > via dma-fence for a couple of reasons:
> >
> > 1) To continue to be able to use the atomic helpers
> > 2) To support cases where display and gpu are different drivers
> >
> > [1] https://patchwork.freedesktop.org/series/90331/
> >
> > v1: https://patchwork.freedesktop.org/series/93035/
> > v2: Move filtering out of later deadlines to fence implementation
> >      to avoid increasing the size of dma_fence
> >
> > Rob Clark (5):
> >    dma-fence: Add deadline awareness
> >    drm/vblank: Add helper to get next vblank time
> >    drm/atomic-helper: Set fence deadline for vblank
> >    drm/scheduler: Add fence deadline support
> >    drm/msm: Add deadline based boost support
> >
> >   drivers/dma-buf/dma-fence.c             | 20 +++++++
> >   drivers/gpu/drm/drm_atomic_helper.c     | 36 ++++++++++++
> >   drivers/gpu/drm/drm_vblank.c            | 31 ++++++++++
> >   drivers/gpu/drm/msm/msm_fence.c         | 76 +++++++++++++++++++++++++
> >   drivers/gpu/drm/msm/msm_fence.h         | 20 +++++++
> >   drivers/gpu/drm/msm/msm_gpu.h           |  1 +
> >   drivers/gpu/drm/msm/msm_gpu_devfreq.c   | 20 +++++++
> >   drivers/gpu/drm/scheduler/sched_fence.c | 25 ++++++++
> >   drivers/gpu/drm/scheduler/sched_main.c  |  3 +
> >   include/drm/drm_vblank.h                |  1 +
> >   include/drm/gpu_scheduler.h             |  6 ++
> >   include/linux/dma-fence.h               | 16 ++++++
> >   12 files changed, 255 insertions(+)
> >
>