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[backend] Fix improper mma->dot shortcut when warpsPerCTA[1] > 1 #4803

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merged 1 commit into from
Sep 25, 2024

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chsigg
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@chsigg chsigg commented Sep 25, 2024

#4492 started causing an issue where chained MMAs on hopper would segfault with 8 warps. It seems that previously this was checked, but the check got removed in this PR and it's still unsupported.

Adding back this check means these MMAs will have to go back to shared memory, but it's better than segfaulting until it's actually supported.

Resolves openxla/xla#17356

triton-lang#4492 started causing an
issue where chained MMAs on hopper would segfault with 8 warps. It seems
that previously this was checked, but the check got removed in this PR
and it's still unsupported.

Adding back this check means these MMAs will have to go back to shared
memory, but it's better than segfaulting until it's actually supported.

Resolves openxla/xla#17356
@Jokeren
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Jokeren commented Sep 25, 2024

Can you copy & paste me the mma->mma instruction and the layouts?

@Jokeren Jokeren self-assigned this Sep 25, 2024
@chsigg
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chsigg commented Sep 25, 2024

Can you copy & paste me the mma->mma instruction and the layouts?

Does openxla/xla#17356 (comment) contain what you need?

@Jokeren
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Jokeren commented Sep 25, 2024

Oh, I think it's mma->dot instead of mma->mma. It's not supposed to be handled by my previous PR. Why did I take it out...I need some further investigation before getting back to you.

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Jokeren commented Sep 25, 2024

I agree with the fix. I actually didn't take out the getWarpsPerCTA, but the previous mmaToMmaShortcut is a misnomer.
@chsigg How about changing the title to:

Fix improper mma->dot shortcut when warpsPerCTA[1] > 1

@chsigg chsigg changed the title [backend] Don't segfault on unsupported mma->mma [backend] Fix improper mma->dot shortcut when warpsPerCTA[1] > 1 Sep 25, 2024
@Jokeren Jokeren merged commit 694719a into triton-lang:main Sep 25, 2024
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@vwbaker vwbaker deleted the warps branch September 26, 2024 07:43
Luosuu pushed a commit to Luosuu/triton that referenced this pull request Nov 13, 2024
…riton-lang#4803)

triton-lang#4492 started causing an
issue where chained MMAs on hopper would segfault with 8 warps. It seems
that previously this was checked, but the check got removed in this PR
and it's still unsupported.

Adding back this check means these MMAs will have to go back to shared
memory, but it's better than segfaulting until it's actually supported.

Resolves openxla/xla#17356

Co-authored-by: Tori <[email protected]>
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Pallas/Triton segfault on H100
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