[PATCH 1/2] drm: Shortcircuit vblank queries

[Chris Wilson]

On Tue, Apr 14, 2015 at 08:22:20PM +0200, Mario Kleiner wrote:
> On 04/05/2015 05:40 PM, Chris Wilson wrote:
> >Avoid adding to the waitqueue and reprobing the current vblank if the
> >caller is only querying the current vblank sequence and timestamp and
> >so we would return immediately.
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >Cc: Daniel Vetter <daniel at ffwll.ch>
> >Cc: Michel Dänzer <michel at daenzer.net>
> >Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> >Cc: Dave Airlie <airlied at redhat.com>,
> >Cc: Mario Kleiner <mario.kleiner.de at gmail.com>
> >---
> >  drivers/gpu/drm/drm_irq.c | 18 ++++++++++--------
> >  1 file changed, 10 insertions(+), 8 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> >index 6f5dc18779e2..ba80b51b4b00 100644
> >--- a/drivers/gpu/drm/drm_irq.c
> >+++ b/drivers/gpu/drm/drm_irq.c
> >@@ -1617,14 +1617,16 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
> >  		vblwait->request.sequence = seq + 1;
> >  	}
> >
> >-	DRM_DEBUG("waiting on vblank count %d, crtc %d\n",
> >-		  vblwait->request.sequence, crtc);
> >-	vblank->last_wait = vblwait->request.sequence;
> >-	DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
> >-		    (((drm_vblank_count(dev, crtc) -
> >-		       vblwait->request.sequence) <= (1 << 23)) ||
> >-		     !vblank->enabled ||
> >-		     !dev->irq_enabled));
> >+	if (vblwait->request.sequence != seq) {
> >+		DRM_DEBUG("waiting on vblank count %d, crtc %d\n",
> >+			  vblwait->request.sequence, crtc);
> >+		vblank->last_wait = vblwait->request.sequence;
> >+		DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
> >+			    (((drm_vblank_count(dev, crtc) -
> >+			       vblwait->request.sequence) <= (1 << 23)) ||
> >+			     !vblank->enabled ||
> >+			     !dev->irq_enabled));
> >+	}
> >
> >  	if (ret != -EINTR) {
> >  		struct timeval now;
> >
> 
> It would be good to have some DRM_DEBUG output for the skip-the-wait
> case as well, so one can still follow from dmesg output when a
> client does a drmWaitVblank call even if it is only a query.

We still have DRM_DEBUG("returning %d to client"), as well as the
drmIoctl:DRM_DEBUG(ioctl->name), is that not sufficient?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre