[Bug 108820] [SKL] (recoverable) GPU hangs in benchmarks using compute shaders with drm-tip v4.20-rc kernels

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108820

--- Comment #14 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Jakub Okoński from comment #12)
> OK, I think I found the precise issue. It occurs when using a control flow
> barrier in the shader with more than 64 items in the workgroup.

Great, thanks!


(In reply to Jakub Okoński from comment #13)
> Vulkan spec defines a minimum of 128 items in the first dimension of a
> workgroup, the driver reports maxComputeWorkGroupSize[0] = 896 so I think my
> application is well behaved in this case and should not hang because of
> limits.

At certain workgroup size thresholds, at least the used SIMD mode can increase
(threshold differs between platforms).

You can check whether there's a change in that between working and non-working
cases with something like this:
  INTEL_DEBUG=cs <your test-case>  2> shader-ir-asm.txt
  grep ^SIMD shader-ir-asm.txt

If SIMD mode doesn't change, what's the diff between the shader IR/ASM output
of the two versions?

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