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Clean up cutlass FP8 Grouped Gemm Kernel Setup #3864

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@jwfromm jwfromm commented Mar 21, 2025

Summary: This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Differential Revision: D71349695

jwfromm added 2 commits March 21, 2025 11:04
Summary:
X-link: facebookresearch/FBGEMM#945


In cases where there are many groups, but few have a non-zero amount of routed tokens, it turns out we pay a high overhead. For example if a single token is routed to one of 128 experts, while the compute is the same as 1 token being routed to one expert the runtime is much lower.

Presumably there are some kernel inefficiencies involved in looping over the empty groups. This diff changes how kernel arguments are set up so that we do grouped gemm over min(total_M, groups). This allows us to ignore many of the groups where no compute is required and improves performance in those cases considerably.

As an example of the effect of this diff, when total_M is 1 and there are 128 groups, latency will be 3X smaller thanks to this change.

Reviewed By: jiawenliu64

Differential Revision: D71510967
Summary: This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Differential Revision: D71349695
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This pull request was exported from Phabricator. Differential Revision: D71349695

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jwfromm added a commit to jwfromm/FBGEMM that referenced this pull request Mar 21, 2025
Summary:
X-link: facebookresearch/FBGEMM#953


This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Differential Revision: D71349695
jwfromm added a commit to jwfromm/FBGEMM that referenced this pull request Mar 24, 2025
Summary:
X-link: facebookresearch/FBGEMM#953


This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Reviewed By: jiawenliu64

Differential Revision: D71349695
jwfromm added a commit to jwfromm/FBGEMM that referenced this pull request Mar 24, 2025
Summary:
X-link: facebookresearch/FBGEMM#953


This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Reviewed By: jiawenliu64

Differential Revision: D71349695
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This pull request has been merged in 27655aa.

q10 pushed a commit to q10/FBGEMM that referenced this pull request Apr 10, 2025
Summary:
Pull Request resolved: facebookresearch/FBGEMM#953

X-link: pytorch#3864

This diff does an overdue refactor and cleanup of the cutlass FP8 Gemm. There's no functional difference but we use more strict and accurate typing and are a bit more careful with buffer allocation.

Reviewed By: jiawenliu64

Differential Revision: D71349695

fbshipit-source-id: d56bbc249dc015b68be688c409fd1b4407abe74f
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3 participants