Re: [PATCH] drm/i915: Boost GPU frequency if we detect outstanding pageflips

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Mar 27, 2014 at 12:01:11PM +0000, Chris Wilson wrote:
> If we hit a vblank and see that have a pageflip queue but not yet
> processed, ensure that the GPU is running at maximum in order to clear
> the backlog. Pageflips are only queued for the following vblank, if we
> miss it, there will be a visible stutter. Boosting the GPU frequency
> doesn't prevent us from missing the target vblank, but it should help
> the subsequent frames hitting theirs.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Does kms_flip already have a synthetic subtest which reliably hits this?
One of the dummy load things should be good enough.

I just want to make sure we exercise this code, actual functional testing
is a bit too tricky I think.
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_display.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index e15b3ab..215526f 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -8960,6 +8960,7 @@ void intel_check_page_flip(struct drm_device *dev, int pipe)
>  	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	unsigned long flags;
> +	bool outstanding;
>  
>  	if (crtc == NULL)
>  		return;
> @@ -8972,7 +8973,11 @@ void intel_check_page_flip(struct drm_device *dev, int pipe)
>  		page_flip_completed(dev_priv, intel_crtc, intel_crtc->unpin_work);
>  		intel_crtc->unpin_work = NULL;
>  	}
> +	outstanding = intel_crtc->unpin_work != NULL;
>  	spin_unlock_irqrestore(&dev->event_lock, flags);
> +
> +	if (outstanding && INTEL_INFO(dev)->gen >= 6)
> +		gen6_rps_boost(dev_priv);
>  }
>  
>  static int intel_crtc_page_flip(struct drm_crtc *crtc,
> -- 
> 1.7.9.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch