Re: [PATCH] drm/i915: Flush outstanding unpin tasks before pageflipping

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

On Fri, Sep 28, 2012 at 12:29:56PM +0100, Chris Wilson wrote:
> If we accumulate unpin tasks because we are pageflipping faster than the
> system can schedule its workers, we can effectively create a
> pin-leak. The solution taken here is to limit the number of unpin tasks
> we have per-crtc and to flush those outstanding tasks if we accumulate
> too many. This should prevent any jitter in the normal case, and also
> prevent the hang if we should run too fast.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=46991
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_display.c |   20 +++++++++++++++-----
>  drivers/gpu/drm/i915/intel_drv.h     |    4 +++-
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 04407fd..14f1b51 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -6310,14 +6310,19 @@ static void intel_unpin_work_fn(struct work_struct *__work)
>  {
>  	struct intel_unpin_work *work =
>  		container_of(__work, struct intel_unpin_work, work);
> +	struct drm_device *dev = work->crtc->dev;
>  
> -	mutex_lock(&work->dev->struct_mutex);
> +	mutex_lock(&dev->struct_mutex);
>  	intel_unpin_fb_obj(work->old_fb_obj);
>  	drm_gem_object_unreference(&work->pending_flip_obj->base);
>  	drm_gem_object_unreference(&work->old_fb_obj->base);
>  
> -	intel_update_fbc(work->dev);
> -	mutex_unlock(&work->dev->struct_mutex);
> +	intel_update_fbc(dev);
> +	mutex_unlock(&dev->struct_mutex);
> +
> +	BUG_ON(atomic_read(&to_intel_crtc(work->crtc)->unpin_work_count) == 0);
> +	atomic_dec(&to_intel_crtc(work->crtc)->unpin_work_count);

AFAICS you always have struct_mutex locked in the relevant functions,
so no need for an atomic variable.

-- 
Ville Syrjälä
Intel OTC