[Intel-gfx] [PATCH 01/25] drm/i915/fbc: wait for a vblank instead of 50ms when enabling
Rodrigo Vivi
rodrigo.vivi at gmail.com
Thu Jan 28 16:07:22 PST 2016
Thanks for all the explanation.
Makes sense now and everything looks fine for me.
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
On Tue, Jan 26, 2016 at 10:08 AM Zanoni, Paulo R <paulo.r.zanoni at intel.com>
wrote:
> Em Ter, 2016-01-26 às 17:44 +0000, Rodrigo Vivi escreveu:
> >
> >
> > On Thu, Jan 21, 2016 at 12:03 PM Paulo Zanoni <paulo.r.zanoni at intel.c
> > om> wrote:
> > > Instead of waiting for 50ms, just wait until the next vblank, since
> > > it's the minimum requirement. The whole infrastructure of FBC is
> > > based
> > > on vblanks, so waiting for X vblanks instead of X milliseconds
> > > sounds
> > > like the correct way to go. Besides, 50ms may be less than a vblank
> > > on
> > > super slow modes that may or may not exist.
> > >
> > > There are some small improvements in PC state residency (due to the
> > > fact that we're now using 16ms for the common modes instead of
> > > 50ms),
> > > but the biggest advantage is still the correctness of being
> > > vblank-based instead of time-based.
> > >
> > > v2:
> > > - Rebase after changing the patch order.
> > > - Update the commit message.
> > > v3:
> > > - Fix bogus vblank_get() instead of vblank_count() (Ville).
> > > - Don't forget to call drm_crtc_vblank_{get,put} (Chris, Ville)
> > > - Adjust the performance details on the commit message.
> > > v4:
> > > - Don't grab the FBC mutex just to grab the vblank (Maarten)
> > >
> > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > > ---
> > > drivers/gpu/drm/i915/i915_drv.h | 2 +-
> > > drivers/gpu/drm/i915/intel_fbc.c | 39
> > > +++++++++++++++++++++++++++++----------
> > > 2 files changed, 30 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.h
> > > b/drivers/gpu/drm/i915/i915_drv.h
> > > index 204661f..d8f21f0 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > @@ -921,9 +921,9 @@ struct i915_fbc {
> > >
> > > struct intel_fbc_work {
> > > bool scheduled;
> > > + u32 scheduled_vblank;
> > > struct work_struct work;
> > > struct drm_framebuffer *fb;
> > > - unsigned long enable_jiffies;
> > > } work;
> > >
> > > const char *no_fbc_reason;
> > > diff --git a/drivers/gpu/drm/i915/intel_fbc.c
> > > b/drivers/gpu/drm/i915/intel_fbc.c
> > > index a1988a4..3993b43 100644
> > > --- a/drivers/gpu/drm/i915/intel_fbc.c
> > > +++ b/drivers/gpu/drm/i915/intel_fbc.c
> > > @@ -381,7 +381,17 @@ static void intel_fbc_work_fn(struct
> > > work_struct *__work)
> > > container_of(__work, struct drm_i915_private,
> > > fbc.work.work);
> > > struct intel_fbc_work *work = &dev_priv->fbc.work;
> > > struct intel_crtc *crtc = dev_priv->fbc.crtc;
> > > - int delay_ms = 50;
> > > + struct drm_vblank_crtc *vblank = &dev_priv->dev-
> > > >vblank[crtc->pipe];
> > > +
> > > + if (drm_crtc_vblank_get(&crtc->base)) {
> > > + DRM_ERROR("vblank not available for FBC on pipe
> > > %c\n",
> > > + pipe_name(crtc->pipe));
> > > +
> > > + mutex_lock(&dev_priv->fbc.lock);
> > > + work->scheduled = false;
> > I couldn't understand this here... doesn't look related to
> > s/time/vblank...
> > could you please explain?
>
> Previously we were just dealing with "wait a certain amount of
> time/jiffies", and for that we can just call the delay/sleep/wait/etc
> calls without needing any get/put calls.
>
> Now we'll wait for a certain number of vblanks, and we need to have the
> vblank interrupts enabled before we can wait for them. That's why we
> have the vblank get/put calls. And since get() can fail, we need an
> error path.
>
> Under normal FBC operation, every vblank get/put call should succeed
> because the pipe's supposed to be running. But in case we actually
> fail to get vblanks, we just exit from the work function. The way we
> signal "the work function is not running" is by setting work->scheduled
> to false.
>
> >
> > > + mutex_unlock(&dev_priv->fbc.lock);
> > > + return;
> > > + }
> > >
> > > retry:
> > > /* Delay the actual enabling to let pageflipping cease and
> > > the
> > > @@ -390,14 +400,16 @@ retry:
> > > * vblank to pass after disabling the FBC before we attempt
> > > * to modify the control registers.
> > > *
> > > - * A more complicated solution would involve tracking
> > > vblanks
> > > - * following the termination of the page-flipping sequence
> > > - * and indeed performing the enable as a co-routine and not
> > > - * waiting synchronously upon the vblank.
> > > - *
> > > * WaFbcWaitForVBlankBeforeEnable:ilk,snb
> > hm... is it still valid for newer platforms or we should put a if gen
> > <=6 on these checks?
>
> I tested this on BDW some time ago, and it seems we don't actually need
> the vblank wait anymore (although I didn't check the docs if we still
> need the wait). But I wanted to convert the code to use vblanks before
> optimizing it more. And the residency impact won't be big.
>
> >
> > > + *
> > > + * It is also worth mentioning that since work-
> > > >scheduled_vblank can be
> > > + * updated multiple times by the other threads, hitting the
> > > timeout is
> > > + * not an error condition. We'll just end up hitting the
> > > "goto retry"
> > > + * case below.
> > > */
> > > - wait_remaining_ms_from_jiffies(work->enable_jiffies,
> > > delay_ms);
> > > + wait_event_timeout(vblank->queue,
> > > + drm_crtc_vblank_count(&crtc->base) != work-
> > > >scheduled_vblank,
> > > + msecs_to_jiffies(50));
> > >
> > > mutex_lock(&dev_priv->fbc.lock);
> > >
> > > @@ -406,8 +418,7 @@ retry:
> > > goto out;
> > >
> > > /* Were we delayed again while this function was sleeping?
> > > */
> > > - if (time_after(work->enable_jiffies +
> > > msecs_to_jiffies(delay_ms),
> > > - jiffies)) {
> > > + if (drm_crtc_vblank_count(&crtc->base) == work-
> > > >scheduled_vblank) {
> > > mutex_unlock(&dev_priv->fbc.lock);
> > > goto retry;
> > > }
> > > @@ -419,6 +430,7 @@ retry:
> > >
> > > out:
> > > mutex_unlock(&dev_priv->fbc.lock);
> > > + drm_crtc_vblank_put(&crtc->base);
> > > }
> > >
> > > static void intel_fbc_cancel_work(struct drm_i915_private
> > > *dev_priv)
> > > @@ -434,13 +446,20 @@ static void
> > > intel_fbc_schedule_activation(struct intel_crtc *crtc)
> > >
> > > WARN_ON(!mutex_is_locked(&dev_priv->fbc.lock));
> > >
> > > + if (drm_crtc_vblank_get(&crtc->base)) {
> > > + DRM_ERROR("vblank not available for FBC on pipe
> > > %c\n",
> > > + pipe_name(crtc->pipe));
> > > + return;
> > > + }
> > > +
> > > /* It is useless to call intel_fbc_cancel_work() in this
> > > function since
> > > * we're not releasing fbc.lock, so it won't have an
> > > opportunity to grab
> > > * it to discover that it was cancelled. So we just update
> > > the expected
> > > * jiffy count. */
> > > work->fb = crtc->base.primary->fb;
> > > work->scheduled = true;
> > > - work->enable_jiffies = jiffies;
> > > + work->scheduled_vblank = drm_crtc_vblank_count(&crtc-
> > > >base);
> > > + drm_crtc_vblank_put(&crtc->base);
> > >
> > > schedule_work(&work->work);
> > > }
> > > --
> > > 2.6.4
> > >
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx at lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > >
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