[Intel-gfx] [PATCH 1/2] drm/i915: Tighting frontbuffer tracking around flips

[Paulo Zanoni]

2014-09-30 17:10 GMT-03:00 Daniel Vetter <daniel.vetter at ffwll.ch>:
> So I think I've spotted a small gap in the frontbuffer tracking
> while discussing the logic with Paulo on irc:
>
> 1. Userspace schedules gpu rendering to the current frontbuffer.
> This gets tracked in dev_priv->fb_tracking.busy_bits.
>
> 2. We pageflip a fully rendered buffer before the frontbuffer
> rendering completes.
>
> 3. The request retiring will never clear busy_bits (since at retire
> time the old frontbuffer won't have obj->frontbuffer_bits set), so
> these bits now are stuck until someone again does a bit of frontbuffer
> tracking.
>
> If we clear stale busy_bits in flip_prepare this gap is closed.
>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

> ---
>  drivers/gpu/drm/i915/intel_frontbuffer.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_frontbuffer.c b/drivers/gpu/drm/i915/intel_frontbuffer.c
> index f74744c091cb..969af6e7b634 100644
> --- a/drivers/gpu/drm/i915/intel_frontbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_frontbuffer.c
> @@ -246,8 +246,9 @@ void intel_frontbuffer_flip_prepare(struct drm_device *dev,
>         struct drm_i915_private *dev_priv = dev->dev_private;
>
>         mutex_lock(&dev_priv->fb_tracking.lock);
> -       dev_priv->fb_tracking.flip_bits
> -               |= frontbuffer_bits;
> +       dev_priv->fb_tracking.flip_bits |= frontbuffer_bits;
> +       /* Remove stale busy bits due to the old buffer. */
> +       dev_priv->fb_tracking.busy_bits &= ~frontbuffer_bits;
>         mutex_unlock(&dev_priv->fb_tracking.lock);
>  }
>
> --
> 2.1.1
>
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-- 
Paulo Zanoni