[Intel-gfx] [PATCH] Revert "drm/i915: enable HiZ Raw Stall Optimization on IVB"

[Daniel Vetter]

On Tue, Mar 04, 2014 at 05:06:22PM +0200, Ville Syrjälä wrote:
> On Tue, Mar 04, 2014 at 10:38:58PM +0800, Chia-I Wu wrote:
> > On Tue, Mar 4, 2014 at 5:41 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > > This reverts commit 116f2b6da868dec7539103574d0421cd6221e931.
> > >
> > > This optimization causes widespread corruption in games, and even in
> > > glxgears, on my ivb:gt1. The corruption appears like z-fighting of
> > > overlapping polygons in the HiZ buffer.
> > >
> > > The observation ties in very closely with the description of the
> > > optimization disabled by default on IVB:
> > >
> > > "The Hierarchical Z RAW Stall Optimization allows non-overlapping
> > > polygons in the same 8x4 pixel/sample area to be processed without
> > > stalling waiting for the earlier ones to write to Hierarchical Z
> > > buffer."
> > >
> > > No reason is given for why it is disabled by default, usually for such
> > > optimizations it is that it is incomplete. However, there is no
> > > indication whether this a gt1 only issue either. Before considering
> > > reenabling this optimization, I would first suggest reproducing the
> > > corruption in piglit.
> > I wonder if Haswell GT1 is affected too (that's in another commit).  I
> > do not own a GT1 for either GEN to verify the issue or to create a
> > sensible piglit test.
> 
> I'm seeing corruption on IVB GT2 as well. I might be more blind than
> Chris or it's less subtle on GT2 since it took me a while to spot it.
> Seems to be easiest to spot in Epic citadel when you go inside the
> temple. I can't spot the same corruption on HSW GT3.

Queued for -next, thanks for the patch. We can tackle hsw when that on
blows up ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch