[Intel-gfx] [PATCH 1/2] drm/i915: Kill i915_gem_execbuffer_wait_for_flips()

[Chris Wilson]

On Wed, 31 Oct 2012 17:18:47 -0700, Eric Anholt <eric at anholt.net> wrote:
> ville.syrjala at linux.intel.com writes:
> 
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >
> > As per Chris Wilson's suggestion make
> > i915_gem_execbuffer_wait_for_flips() go away.
> >
> > This was used to stall the GPU ring while there are pending
> > page flips involving the relevant BO. Ie. while the BO is still
> > being scanned out by the display controller.
> >
> > The recommended alternative is to use the page flip events to
> > wait for the page flips to fully complete before reusing the BO
> > of the old front buffer. Or use more buffers.
> 
> So, after this change, if userland submits an execbuf between having
> requested a pageflip and the vblank that the flip shows up on, does that
> exec block?

The code itself is dysfunctional and would cause a GPU hang on snb/ivb.
Why should the kernel be imposing a policy upon userspace where none is
required?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre