[Bug 108875] Invalid subgroupSize for Intel GPU

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Tue Nov 27 14:53:00 UTC 2018


--- Comment #8 from Jason Ekstrand <jason at jlekstrand.net> ---
> The subgroupSize is 32 only for shaders with local group size more than 896.

Correct.  We have to run 32-wide when you get very large local group sizes in
order to fit the entire group on the GPU at once.  Otherwise, we usually run 16
or 8-wide depending on register usage.

Don't worry; you are not the first person to have this problem.  I can't speak
for D3D12 but for Vulkan we do have something in the works which provides more
explicit control over subgroup sizes so that you can really know what you're
getting.  Unfortunately, I can't really provide a timeline as to when it will
be available.

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