[https://nvbugs/5676748][fix] Cherry-pick #9336: Fix mismatched nvfp4 gemm sf shape.

[hyukn]

We find that release/1.1 also has this issue and may have a potential perf drop.

Summary by CodeRabbit

• Refactor
  • Optimized internal tensor allocation for NVFP4 uint8 operations in attention processing, improving memory layout efficiency.

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[hyukn]

/bot run --disable-fail-fast

[coderabbitai[bot]]

📝 Walkthrough

Walkthrough

Modified the scaling factors buffer allocation in the NVFP4 uint8 code path of the attention backend. Changed from using a computed 2D shape to directly allocating a flattened 1D tensor with padded dimensions, altering the memory layout strategy.

Changes

Cohort / File(s)	Summary
NVFP4 scaling factors buffer allocation tensorrt_llm/_torch/attention_backend/trtllm.py	Modified create_output function to allocate scaling factors as a flat 1D tensor using computed padded dimensions (padded_row × padded_col) instead of using compute_swizzled_sf_shape() for 2D shape construction

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Review the memory layout implications of changing from 2D shaped allocation to 1D flattened allocation
• Verify that the padded dimension computation (padded_row, padded_col) correctly replaces the previous compute_swizzled_sf_shape() logic
• Confirm that downstream code consuming this buffer still functions correctly with the flattened layout

Pre-merge checks and finishing touches

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Description check	⚠️ Warning	The PR description lacks critical required sections. It only contains a brief statement about the issue but is missing proper sections for Description, Test Coverage, and incomplete PR Checklist details.	Fill in the Description section explaining what the issue is and the solution. Document relevant test coverage in the Test Coverage section. Verify and complete the PR Checklist items, especially noting what testing was performed.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies a specific bug fix (mismatched nvfp4 gemm sf shape) with a bug reference and indicates it's a cherry-pick, directly matching the code changes.

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[tensorrt-cicd]

PR_Github #25691 [ run ] triggered by Bot. Commit: 819eb39

[tensorrt-cicd]

PR_Github #25691 [ run ] completed with state SUCCESS. Commit: 819eb39 /LLM/release-1.1/L0_MergeRequest_PR pipeline #527 completed with status: 'SUCCESS' Pipeline passed with automatic retried tests. Check the rerun report for details.

[hyukn]

/bot skip --comment "Pipeline has already been cleaned and only change the pre-commit configs."

[tensorrt-cicd]

PR_Github #25816 [ skip ] triggered by Bot. Commit: 287fed2

[tensorrt-cicd]

PR_Github #25816 [ skip ] completed with state SUCCESS. Commit: 287fed2 Skipping testing for commit 287fed2