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[None][fix] Pass alpha through SM107 scaled_mm compilation - #19150

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peaceh-nv:peaceh/fix-scaled-mm-alpha

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@peaceh-nv peaceh-nv commented Sep 14, 2026

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Dev Engineer Review

The Rubin scaled_mm path now passes alpha_tensor as an explicit compiled-kernel parameter. It also accepts batch_size and optional wrapper layouts. The Blackwell scaled_mm helper was removed.

Verify caller imports, SM107 compilation, alpha scaling, default and explicit layouts, and batched execution.

QA Engineer Review

No test changes.

Per-File QA Perspective

  • tensorrt_llm/_torch/cute_dsl_kernels/blackwell/dense_blockscaled_gemm_persistent.py: The public scaled_mm helper was removed. Verify that no caller still imports or invokes it from the Blackwell module.
  • tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py: SM107 compilation now includes runtime alpha_tensor, matrix and scale-factor dimensions, and optional batch_size. Verify alpha propagation, layout handling, GEMM/BMM execution, and split-K behavior.

Pass the runtime alpha tensor before the layout and problem-size arguments
when compiling the SM107 pointer interface. Clarify the helper's SM107 type
contract and reuse it from the Rubin benchmark instead of duplicating its
compilation logic.

Refs NVIDIA#18334.

Signed-off-by: peaceh <103117813+peaceh-nv@users.noreply.github.com>
@peaceh-nv
peaceh-nv requested a review from farazkh80 September 14, 2026 09:47
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peaceh-nv requested a review from a team as a code owner September 14, 2026 09:47
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peaceh-nv requested a review from rosong11 September 14, 2026 09:47
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Walkthrough

The Rubin GEMM path now compiles through its wrapper with explicit dimensions, layouts, and batch size. The Blackwell scaled_mm helper and its helper-only imports are removed. Benchmark paths pass the updated wrapper arguments.

Changes

Rubin GEMM compilation

Layer / File(s) Summary
Blackwell helper removal
tensorrt_llm/_torch/cute_dsl_kernels/blackwell/dense_blockscaled_gemm_persistent.py
The public scaled_mm helper and imports used only by it are removed.
Rubin wrapper contract
tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py
The wrapper accepts optional layouts and preserves default layout selection when layouts are omitted. scaled_mm compiles the wrapper with matrix dimensions, scale-factor dimensions, leading dimension, layouts, and batch size.
Benchmark argument updates
tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py
The emulated, reference, split-K, and generated benchmark paths pass the updated wrapper arguments. The reference result remains alpha-scaled.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Suggested reviewers: bowenfu

Merge Risk: ⚪ Minimal · up to 966e2

The updated GEMM compilation paths consistently pass alpha, dimensions, layouts, and batch configuration, with no concrete merge-blocking issue identified.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name Status Explanation Resolution
Description check ⚠️ Warning No pull request description was provided. The required Description, Test Coverage, and PR Checklist information is missing. Add a pull request description that explains the issue and solution, lists relevant tests and coverage, and addresses the applicable PR checklist items.
Docstring Coverage ⚠️ Warning Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 7 functions across 2 files. Write docstrings for the functions missing them to satisfy the coverage threshold.
✅ Passed checks (3 passed)
Check name Status Explanation
Title check ✅ Passed The title follows the required [None][type] format and clearly states the main change: passing alpha through SM107 scaled_mm compilation.
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.
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Confirmed this resolves #18334. alpha_tensor now lands in the right positional slot matching the SM107 kernel's __call__. A couple of small follow-ups below.

Comment thread tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py Outdated

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Approving with small comments. Thanks!

Move scaled_mm into the Rubin module alongside its only caller and reject
kernels with incompatible call signatures before compilation. Use alpha=0.5
in the benchmark reference check and scale the reference accordingly.

Validation on hecate0233 (SM107): six NVFP4 GPU cases covering FP16/BF16,
GEMM/BMM and split-K; mixed-cluster rejection; ignored-alpha negative check.
All applicable pre-commit checks passed.

Signed-off-by: peaceh <103117813+peaceh-nv@users.noreply.github.com>

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Actionable comments posted: 1

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Inline comments:
In
`@tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py`:
- Line 3730: Update scaled_mm to compile and invoke gemm_obj.wrapper rather than
the direct gemm_obj contract, passing matrix and scale-factor dimensions before
alpha_tensor in the required signature order. Update the benchmark caller
accordingly, and add a regression exercising this wrapper path with
alpha_tensor=0.5.

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  • tensorrt_llm/_torch/cute_dsl_kernels/blackwell/dense_blockscaled_gemm_persistent.py
  • tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py

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Comment thread tensorrt_llm/_torch/cute_dsl_kernels/rubin/dense_blockscaled_gemm_persistent.py Outdated
Use runtime Int64 matrix and scale-factor dimensions and alpha in the
wrapper signature order. Specialize the batch size at compilation and
update the reference, benchmark, and split-K launches to the wrapper ABI.

Allow an optional compile-time layout override so the helper preserves
its layout mapping while existing custom-op wrapper calls keep their
default behavior. Retain the non-unit alpha reference check.

Refs NVIDIA#18334.

Validation: all applicable pre-commit hooks passed. GPU tests were not rerun.
Signed-off-by: peaceh <103117813+peaceh-nv@users.noreply.github.com>
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/bot run

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PR_Github #73431 [ run ] triggered by Bot. Commit: 966e2fa Link to invocation

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PR_Github #73431 [ run ] completed with state SUCCESS. Commit: 966e2fa
/LLM/main/L0_MergeRequest_PR pipeline #60349 completed with status: 'FAILURE'

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/bot run --disable-fail-fast

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/bot run --disable-fail-fast

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PR_Github #73694 [ run ] triggered by Bot. Commit: 966e2fa Link to invocation

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3 participants