[PATCH 1/2] drm: Shortcircuit vblank queries

[Mario Kleiner]

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.

Other than that, this one [1/2] is

Reviewed-and-tested-by: Mario Kleiner <mario.kleiner.de at gmail.com>

-mario