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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [SKL] (recoverable) GPU hangs in benchmarks using compute shaders with drm-tip v4.20-rc kernels"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108820#c14">Comment # 14</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [SKL] (recoverable) GPU hangs in benchmarks using compute shaders with drm-tip v4.20-rc kernels"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108820">bug 108820</a>
from <span class="vcard"><a class="email" href="mailto:eero.t.tamminen@intel.com" title="Eero Tamminen <eero.t.tamminen@intel.com>"> <span class="fn">Eero Tamminen</span></a>
</span></b>
<pre>(In reply to Jakub Okoński from <a href="show_bug.cgi?id=108820#c12">comment #12</a>)
<span class="quote">> 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.</span >
Great, thanks!
(In reply to Jakub Okoński from <a href="show_bug.cgi?id=108820#c13">comment #13</a>)
<span class="quote">> 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.</span >
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?</pre>
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