Re: [PATCH 09/12] drm/i915: wait for a vblank instead of 50ms when enabling FBC

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Nov 13, 2015 at 11:20:19PM +0200, Ville Syrjälä wrote:
> On Fri, Nov 13, 2015 at 09:03:43PM +0000, Chris Wilson wrote:
> > On Fri, Nov 13, 2015 at 05:53:41PM -0200, Paulo Zanoni wrote:
> > > Instead of waiting for 50ms, just wait until the next vblank, since
> > > it's the minimum requirement.
> > > 
> > > This moves PC7 residency on my specific BDW machine running Cinnamon
> > > from 60-70% to 84-89%. Without FBC, I get 20-25%. I'm using a
> > > 3200x1800 eDP panel. Notice: this was the case when the patch was
> > > originally proposed, the order of the FBC patches changed since then,
> > > so the actual numbers might be slightly different now.
> > > 
> > > v2:
> > >   - Rebase after changing the patch order.
> > >   - Update the commit message.
> > > 
> > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_drv.h  |  2 +-
> > >  drivers/gpu/drm/i915/intel_fbc.c | 12 +++---------
> > >  2 files changed, 4 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > > index 9418bd5..ea08714 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > @@ -919,9 +919,9 @@ 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 aa82075..72de8a1 100644
> > > --- a/drivers/gpu/drm/i915/intel_fbc.c
> > > +++ b/drivers/gpu/drm/i915/intel_fbc.c
> > > @@ -391,7 +391,6 @@ 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;
> > > -	unsigned long delay_jiffies = msecs_to_jiffies(50);
> > >  
> > >  retry:
> > >  	/* Delay the actual enabling to let pageflipping cease and the
> > > @@ -400,14 +399,9 @@ 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
> > >  	 */
> > > -	wait_remaining_ms_from_jiffies(work->enable_jiffies, delay_jiffies);
> > > +	intel_wait_for_vblank(dev_priv->dev, crtc->pipe);
> > >  
> > >  	mutex_lock(&dev_priv->fbc.lock);
> > >  
> > > @@ -416,7 +410,7 @@ retry:
> > >  		goto out;
> > >  
> > >  	/* Were we delayed again while this function was sleeping? */
> > > -	if (time_after(work->enable_jiffies + delay_jiffies, jiffies)) {
> > > +	if (drm_crtc_vblank_get(&crtc->base) == work->scheduled_vblank) {
> > >  		mutex_unlock(&dev_priv->fbc.lock);
> > >  		goto retry;
> > >  	}
> > > @@ -449,7 +443,7 @@ static void intel_fbc_schedule_activation(struct intel_crtc *crtc)
> > >  	 * jiffy count. */
> > >  	work->fb = crtc->base.primary->fb;
> > >  	work->scheduled = true;
> > > -	work->enable_jiffies = jiffies;
> > > +	work->scheduled_vblank = drm_crtc_vblank_count(&crtc->base);
> > 
> > Isn't the frame counter only incrementing whilst the vblank IRQ is
> > enabled? Ville?
> 
> I see a "+ if (drm_crtc_vblank_get(" earlier.

Hmm. Actually it's doing
"drm_crtc_vblank_get(&crtc->base) == work->scheduled_vblank)"
which looks rather like nonsense.

Not sure what the intention here was...

-- 
Ville Syrjälä
Intel OTC
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