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@LucasWilkinson LucasWilkinson commented Jul 5, 2025

Essential Elements of an Effective PR Description Checklist

  • The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
  • The test plan, such as providing test command.
  • The test results, such as pasting the results comparison before and after, or e2e results
  • (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

Fix:

[ImportError: /home/lwilkinson/code/vllm2/vllm/_C.abi3.so: undefined symbol: _Z35cutlass_blockwise_scaled_grouped_mmRN2at6TensorERKS0_S3_S3_S3_S3_S3_]

when building from source on hopper systems.

Caused by #19757 conditionally compiling csrc/quantization/cutlass_w8a8/moe/blockwise_scaled_group_mm_sm100.cu but did not make the linkage conditional.

Also adding my self as a CMakeList code owner to get more eyes and hopefully catch these things early (please let me know if you'd prefer the to be a separate PR .

Test Plan

  • For hopper systems test that vLLM starts up after a local build
  • For Blackwell systems test that python -m pytest tests/kernels/moe/test_cutlass_grouped_gemm.py still passes

Test Result

  • For hopper systems vLLM now starts up after a local build
  • For Blackwell systems confirmed python -m pytest tests/kernels/moe/test_cutlass_grouped_gemm.py passes

(Optional) Documentation Update

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
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Summary of Changes

Hello @LucasWilkinson, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily addresses a critical ImportError that prevented successful builds on Hopper systems by correcting the conditional registration of a specific CUTLASS kernel. It refactors the PyTorch operator binding mechanism for this kernel to align with its conditional compilation, ensuring symbol availability. Additionally, it includes an administrative update to code ownership for build-related files.

Highlights

  • Bug Fix: ImportError on Hopper Systems: This pull request resolves an ImportError (specifically, an undefined symbol error for cutlass_blockwise_scaled_grouped_mm) that occurred when building the project from source on Hopper (SM100) systems. The issue was traced to a mismatch where the kernel was conditionally compiled for SM100 but its PyTorch operator registration was not similarly conditional, leading to a missing symbol at runtime.
  • Refactor: Conditional PyTorch Op Registration: The core fix involves moving the PyTorch operator registration for cutlass_blockwise_scaled_grouped_mm from the central csrc/torch_bindings.cpp file to its specific implementation file, csrc/quantization/cutlass_w8a8/moe/blockwise_scaled_group_mm_sm100.cu. This ensures that the operator is only registered when its corresponding CUDA implementation is compiled, resolving the symbol lookup error.
  • Administrative: Code Ownership Update: As a secondary change, the author, LucasWilkinson, has been added as a code owner for CMakeLists.txt. This aims to improve oversight and proactively catch similar build-related issues in the future.
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@mergify mergify bot added the ci/build label Jul 5, 2025
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Code Review

This pull request correctly fixes an ImportError by moving the registration of a conditionally compiled CUDA kernel into its source file, ensuring it's only registered when compiled. The changes in ops.h, torch_bindings.cpp, and the .cu file are logical and address the issue. I've added a comment regarding code formatting in the new registration block to improve consistency and maintainability.

@LucasWilkinson LucasWilkinson changed the title [BugFix] Fix: ImportError: .../_C.abi3.so: undefined symbol: _Z35cutlass_blockwise_scaled_grouped_mmRN2at6TensorERKS0_S3_S3_S3_S3_S3_ when building on hopper systems [BugFix] Fix: ImportError when building on hopper systems Jul 5, 2025
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
@LucasWilkinson LucasWilkinson marked this pull request as ready for review July 5, 2025 19:19
@LucasWilkinson LucasWilkinson added the ready ONLY add when PR is ready to merge/full CI is needed label Jul 5, 2025
@DarkLight1337 DarkLight1337 merged commit 40b86aa into vllm-project:main Jul 6, 2025
109 of 110 checks passed
Pradyun92 pushed a commit to Pradyun92/vllm that referenced this pull request Aug 6, 2025
…ct#20513)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
npanpaliya pushed a commit to odh-on-pz/vllm-upstream that referenced this pull request Aug 6, 2025
jinzhen-lin pushed a commit to jinzhen-lin/vllm that referenced this pull request Aug 9, 2025
…ct#20513)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Signed-off-by: Jinzhen Lin <linjinzhen@hotmail.com>
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