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

[Chris Wilson]

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 at 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?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre