[Intel-gfx] [PATCH] drm/i915: Add OACONTROL to the command parser register whitelist.

[Chris Wilson]

On Fri, May 16, 2014 at 12:34:08PM -0700, Jesse Barnes wrote:
> On Fri, 16 May 2014 20:20:50 +0100
> Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > We haven't even fixed the major regression from enabling FBC. What's
> > another massive slowdown?
> 
> I thought you had that fixed in the X driver by avoiding front buffer
> rendering altogether.  If that's the case we just need an ioctl to opt
> out of front buffer tracking, right?  Presumably that flag would follow
> the current DRM_MASTER process...

No. All rendering triggers FBC updates. Ville has patches to fix the
majority of that with only nuking FBC when front buffer rendering. (Note
that games aren't usually affected by this because FBC is disabled by
pageflipping.) The overhead could probably be reduced further by periodic
nuking the FBC like (ideally) PSR. And yes X can avoid front buffer
rendering altogether. The remaining challenge is to know when to enable it
(the kernel doesn't give us any information about FBC or PSR after setting a
mode) and when not, i.e. there is already a pageflipping compositor.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre