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

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Fri, 16 May 2014 20:49:30 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> 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@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.

I thought there was a control bit for when the nuke occurred?  If not,
yeah I guess we have to go with a sw approach...

-- 
Jesse Barnes, Intel Open Source Technology Center