[Bug 102272] [BXT] up to 6% performance drop with "i965: Set "Subslice Hashing Mode" to 16x16 on Apollolake"

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102272

--- Comment #1 from Eero Tamminen <eero.t.tamminen at intel.com> ---
I.e. it seems that things depending on raw sampler throughput have perf drops,
and everything that is completely memory bandwidth bound improves a bit.

If latter gets verified by bisection, I'm not sure whether anything should be
done about this bug, as bandwidth limitations should be more common for
real-world use-cases than being purely sampler limited.

Both FurMark and GiMark use anisotropic filtering, but I think changing hash
mode for a draw, based on sampling mode, would have too much overhead.


Terrain tessellation doesn't use costly filtering, so for a drop in that I
don't have yet a good explanation.

It's possible that using larger (16x16) area for the cross-slice load balancing
checkerboard works worse for very small triangles, but impact "should" then be
visible both in instancing & tessellation shader terrain tests, as both run
about same amount of pixel shader instances, look same and have identical pixel
shaders.  Maybe different vertex order explain that difference.

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