[Bug] test_nvfp4_gather_grouped_gemm_act_fusion_blackwell flaky on B300: ~0.05% mismatch vs rtol 1e-4, varying parametrizations
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Description
Summary
unittest/_torch/thop/parallel/test_cute_dsl_moe.py::test_nvfp4_gather_grouped_gemm_act_fusion_blackwell fails intermittently in pre-merge stage B300-PyTorch-2 with:
Exception: Mismatch percentage is ~0.05 for rtol 0.000100
Observed twice on unrelated PR #15730 with different parametrizations:
[8192-8-1-256-relu2]— L0_MergeRequest_PR build 47303 (mismatch 0.050421)[128-1-32-128-relu2]— L0_MergeRequest_PR build 47362 (mismatch 0.054688)
Both runs were on current main bases; the test passes in other runs, so this is a marginal-tolerance flake on B300 rather than a deterministic regression.
Impact
Pre-merge blocker (fail-fast) for unrelated PRs when B300-PyTorch-2 is selected and the tolerance coin-flip loses.
Ask
Loosen rtol / deflake the kernel comparison for B300, or waive until fixed.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with unittest/_torch/thop/parallel/test_cute_dsl_moe.py::test_nvfp4_gather_grouped_gemm_act_fusion_blackwell and reproduce the reported parametrizations on B300-PyTorch-2. Inspect the comparison tolerance and kernel test behavior, then validate the chosen deflake or tolerance change across the affected cases. Done means intermittent failures no longer block unrelated pre-merge runs.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python, pytorch
- Domain
- machine-learning, testing-qa
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 55/100