From: Daniel Vetter <daniel@ffwll.ch>
To: Rob Clark <robdclark@gmail.com>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
freedreno <freedreno@lists.freedesktop.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
Rob Clark <robdclark@chromium.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <mripard@kernel.org>,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@linux.ie>,
open list <linux-kernel@vger.kernel.org>,
Matthew Brost <matthew.brost@intel.com>,
Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [RFC 2/3] drm/atomic: Call dma_fence_boost() when we've missed a vblank
Date: Tue, 1 Jun 2021 16:18:52 +0200 [thread overview]
Message-ID: <YLZBzKlb7xpJaG4+@phenom.ffwll.local> (raw)
In-Reply-To: <CAF6AEGv470U7fujLrJOE8fJh1o-BW3=mOpKJ45FFz=Xb8Q0D6A@mail.gmail.com>
On Sun, May 30, 2021 at 07:33:57AM -0700, Rob Clark wrote:
> On Thu, May 20, 2021 at 9:29 AM Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> > On Wed, May 19, 2021 at 11:38:53AM -0700, Rob Clark wrote:
> > > From: Rob Clark <robdclark@chromium.org>
> > >
> > > Signed-off-by: Rob Clark <robdclark@chromium.org>
> > > ---
> > > drivers/gpu/drm/drm_atomic_helper.c | 11 +++++++++++
> > > 1 file changed, 11 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > index 560aaecba31b..fe10fc2e7f86 100644
> > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > @@ -1435,11 +1435,15 @@ int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
> > > int i, ret;
> > >
> > > for_each_new_plane_in_state(state, plane, new_plane_state, i) {
> > > + u64 vblank_count;
> > > +
> > > if (!new_plane_state->fence)
> > > continue;
> > >
> > > WARN_ON(!new_plane_state->fb);
> > >
> > > + vblank_count = drm_crtc_vblank_count(new_plane_state->crtc);
> > > +
> > > /*
> > > * If waiting for fences pre-swap (ie: nonblock), userspace can
> > > * still interrupt the operation. Instead of blocking until the
> > > @@ -1449,6 +1453,13 @@ int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
> > > if (ret)
> > > return ret;
> > >
> > > + /*
> > > + * Check if we've missed a vblank while waiting, and if we have
> > > + * signal the fence that it's signaler should be boosted
> > > + */
> > > + if (vblank_count != drm_crtc_vblank_count(new_plane_state->crtc))
> > > + dma_fence_boost(new_plane_state->fence);
> >
> > I think we should do a lot better here:
> > - maybe only bother doing this for single-crtc updates, and only if
> > modeset isn't set. No one else cares about latency.
> >
> > - We should boost _right_ when we've missed the frame, so I think we
> > should have a _timeout wait here that guesstimates when the vblank is
> > over (might need to throw in a vblank wait if we missed) and then boost
> > immediately. Not wait a bunch of frames (worst case) until we finally
> > decide to boost.
>
> I was thinking about this a bit more.. How about rather than calling
> some fence->op->boost() type thing when we are about to miss a vblank
> (IMO that is also already too late), we do something more like
> fence->ops->set_deadline() before we even wait?
Hm yeah that sounds like a clean idea.
Even more, why not add the deadline/waiter information to the callback
we're adding? That way drivers can inspect it whenever they feel like and
don't have to duplicate the tracking. And it's probably easier to
tune/adjust to the myriads of use-cases (flip target miss, userspace wait,
wakeup boost maybe too ...).
I like this direction a lot more than what we discussed with post-miss
hints thus far.
> It's probably a bit impossible for a gpu driver to really predict how
> long some rendering will take, but other cases like video decoder are
> somewhat more predictable.. the fence provider could predict given the
> remaining time until the deadline what clk rates are required to get
> you there.
Well if we do have a deadline the driver can note that in its scheduler
and arm a driver to kick the clocks. Or maybe use past history to do this
upfront.
-Daniel
>
> BR,
> -R
>
>
> >
> > Otherwise I really like this, I think it's about the only real reason i915
> > isn't using atomic helpers.
> >
> > Also adding Matt B for this topic.
> > -Daniel
> >
> > > +
> > > dma_fence_put(new_plane_state->fence);
> > > new_plane_state->fence = NULL;
> > > }
> > > --
> > > 2.30.2
> > >
> >
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2021-06-01 14:19 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 18:38 [RFC 0/3] dma-fence: Add a "boost" mechanism Rob Clark
2021-05-19 18:38 ` [RFC 1/3] dma-fence: Add boost fence op Rob Clark
2021-05-20 6:46 ` Christian König
2021-05-20 14:07 ` Rob Clark
2021-05-20 14:11 ` Christian König
2021-05-20 14:54 ` Rob Clark
2021-05-20 16:01 ` [Linaro-mm-sig] " Christian König
2021-05-20 16:34 ` Daniel Vetter
2021-05-20 16:40 ` Christian König
2021-05-20 17:08 ` Daniel Vetter
2021-05-21 7:43 ` Christian König
2021-05-21 14:21 ` Daniel Vetter
2021-05-20 16:25 ` Daniel Vetter
2021-05-19 18:38 ` [RFC 2/3] drm/atomic: Call dma_fence_boost() when we've missed a vblank Rob Clark
2021-05-20 16:29 ` Daniel Vetter
2021-05-30 14:33 ` Rob Clark
2021-06-01 14:18 ` Daniel Vetter [this message]
2021-06-01 15:46 ` Rob Clark
2021-06-01 16:11 ` Daniel Vetter
2021-05-19 18:38 ` [RFC 3/3] drm/msm: Wire up gpu boost Rob Clark
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