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

[Chia-I Wu]

On Wed, Mar 5, 2014 at 2:38 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> 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 ...
I've created a simple demo that demonstrates the problem on IVB GT2,
FWIW.  The patch is against mesa-demos.  Not sure if there is a need
to make it a piglit test.



> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
olv at LunarG.com
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