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[#20515][fix] Pass the environment's nvcc to the trtllm-gen FMHA JIT - #20521
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…A JIT The trtllm-gen JIT queries the nvcc version even when it compiles with NVRTC, and uses /usr/local/cuda/bin/nvcc unless the generated config sets nvccPath. Resolve nvcc from CUDA_HOME, CUDA_PATH, then PATH, and emit it as nvccPath; keep the archive default when none is found. Signed-off-by: Zihua Wu <13583761+lucifer1004@users.noreply.github.com>
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WalkthroughThe FMHA kernel configuration searches for an executable ChangesFMHA NVCC path configuration
Priority: ➖ Normal Estimated code review effort: 2 (Simple) | ~10 minutes Change: Bug fix · Severity of issue fixed: Medium Suggested reviewers: Merge Risk: ⚪ Minimal · up to
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| Check name | Status | Explanation | Resolution |
|---|---|---|---|
| Linked Issues check |  |
The change implements the #20515 stopgap for ordinary POSIX paths. getNvccPath() checks CUDA_HOME, CUDA_PATH, and PATH once per process. populateJsonConfig() emits nvccPath. However, the e… |
Reject every JSON control character U+0000 through U+001F in nvccPath, in addition to " and \\\\. Add focused automated coverage for a control-character path if the test setup permits it. |
| Docstring Coverage | |
Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files. | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Title check The title clearly and concisely describes the primary fix: passing the environment's nvcc path to the trtllm-gen FMHA JIT. Description check The description explains the problem, solution, scope, test coverage, limitations, and checklist status. It provides sufficient detail for review. Out of Scope Changes check The whole-PR diff changes only fmhaKernels.h. The environment lookup andnvccPathemission directly implement the#20515stopgap. No unrelated product behavior, dependency, or public API change is…Full details: Out of Scope Changes check
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Explanation
The whole-PR diff changes only
fmhaKernels.h. The environment lookup andnvccPathemission directly implement the#20515stopgap. No unrelated product behavior, dependency, or public API change is shown.
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Full details: Linked Issues check
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Explanation
The change implements the
#20515stopgap for ordinary POSIX paths.getNvccPath()checksCUDA_HOME,CUDA_PATH, andPATHonce per process.populateJsonConfig()emitsnvccPath. However, the emission guard rejects only"and\\. A path containing another JSON control character, such as newline or tab, can be emitted without escaping and can produce invalid JSON. The prior assessment identified this same unmet requirement, and the current diff does not fix it.Resolution
Reject every JSON control character U+0000 through U+001F in
nvccPath, in addition to"and\\. Add focused automated coverage for a control-character path if the test setup permits it.
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Actionable comments posted: 1
- 🪄 Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at
@cpp/tensorrt_llm/kernels/trtllmGenKernels/fmha/fmhaKernels.h:
- Line 853: Update the candidate-file check in getNvccPath to use the
std::filesystem::is_regular_file overload that accepts an error_code, and treat
a status-check error as a failed candidate so discovery continues to later
CUDA_HOME, CUDA_PATH, and PATH candidates. Preserve the existing
executable-permission check for valid regular files.
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cpp/tensorrt_llm/kernels/trtllmGenKernels/fmha/fmhaKernels.h
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@yunruis, could you help to review this PR as trt-llm-torch-attention-devs? Thanks~ Assignment explanation
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Signed-off-by: Zihua Wu <13583761+lucifer1004@users.noreply.github.com>
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Test report for 12afcb1 (PR diff applied on a build from an earlier main, Vera Rubin SM 10.7, single GPU, no
In the last two cases the new code skips the unreadable candidate and uses the next |
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Add more nvcc search path. LGTM
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Automatically added "ci: full pre-merge approved" because this PR has satisfied the required GitHub review approvals. Unresolved review conversations and other required checks remain independent merge requirements. |
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@yunruis thanks for the review. Starting CI. The GPU test report for the current head 12afcb1 (including the unreadable-directory cases from the CodeRabbit comment) is here: #20521 (comment) |
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/bot run |
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PR_Github #78943 [ run ] triggered by Bot. Commit: |
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PR_Github #78943 [ run ] completed with state
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CI #78943 failed outside this PR (it only changes how the trtllm-gen FMHA JIT finds nvcc):
Re-running. |
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PR_Github #79018 [ run ] triggered by Bot. Commit: |
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CI #79018 did not get to run tests: the |
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PR_Github #79043 [ run ] triggered by Bot. Commit: |
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PR_Github #79043 [ run ] completed with state
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Signed-off-by: Zihua Wu <13583761+lucifer1004@users.noreply.github.com>
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CI #79043 failed outside this PR. The only failing stage is I merged current main (b0534d4, no conflicts; the PR diff is unchanged and main has not touched |
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PR_Github #79104 [ run ] triggered by Bot. Commit: |
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CI #79104 failed outside this PR. The only hard failure is on With main merged, |
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PR_Github #79176 [ run ] triggered by Bot. Commit: |
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CI #79176 failed outside this PR. The only hard failure is on
The other non-green stages were aborted by fail-fast. Re-running. |
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PR_Github #79230 [ run ] triggered by Bot. Commit: |
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PR_Github #79230 [ run ] completed with state
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Signed-off-by: Zihua Wu <13583761+lucifer1004@users.noreply.github.com>
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The last CI run failed for reasons unrelated to this PR:
I merged current main (557ddca) to pick up that waive. The PR diff is unchanged: it only changes how the FMHA JIT path locates nvcc. Re-running. |
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PR_Github #79353 [ run ] triggered by Bot. Commit: |
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The last CI run failed for infrastructure reasons and no tests ran on the failing stages. Every DGX_B200 single-GPU stage failed during setup: the SSH connection to the cluster's Slurm login node kept closing, the retries ran out, and fail-fast then aborted the remaining stages. No test failures were reported. Other PRs' runs over the same window hit the same B200 setup failure. Nothing in this PR is involved, since it fails before any build artifact is used. Re-running. |
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PR_Github #79400 [ run ] triggered by Bot. Commit: |
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The last run failed again for the same infrastructure reason: the DGX_B200 stages could not reach the Slurm login node, and fail-fast then aborted the rest. The other failure was a timing-sensitive CPU unit test, |
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PR_Github #79677 [ run ] triggered by Bot. Commit: |
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PR_Github #79677 [ run ] completed with state
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This run failed before any related test could fail. One RTX Pro 6000 stage spent its whole time budget installing Python dependencies: package downloads on that runner were running at ~180 kB/s. It hit the stage timeout before running any tests, and fail-fast then interrupted every other stage. The few tests reported as failed were the ones in flight when they were killed ("terminated unexpectedly"), plus a timeout in a disaggregated router test on A10 that also fails intermittently on other PRs. None of them run the trtllm-gen FMHA JIT path this PR touches. Re-running. |
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PR_Github #79697 [ run ] triggered by Bot. Commit: |
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PR_Github #79697 [ run ] completed with state |
Description
Fixes #20515 on the TensorRT-LLM side.
The trtllm-gen FMHA JIT in the prebuilt
libTrtLlmGen.arunsnvcc --versionbefore it compiles a kernel, also when it compiles with NVRTC. It runs thenvccPathfrom the generated kernel config, which defaults to/usr/local/cuda/bin/nvcc, andpopulateJsonConfignever set it. So in any environment where the toolkit is not at/usr/local/cuda(for example conda or pixi environments), every NVRTC FMHA kernel fails withCannot parse NVCC version from /usr/local/cuda/bin/nvcc, even whenCUDA_HOMEis set andnvccis onPATH. In serving this fails executor creation during the FMHA JIT warmup.This PR resolves
nvcconce per process from$CUDA_HOME/bin/nvcc, then$CUDA_PATH/bin/nvcc, then the firstnvcconPATH, and emits it as"nvccPath"in the generated config. If none is found, the field is omitted and the archive keeps its default, so environments that rely on/usr/local/cudabehave as before. A path that would need JSON escaping is not emitted either.The archive could still skip
nvccentirely whenusesNvRtcis set (it only needs the version), as suggested in #20515; that part needs an archive update and is not in this PR.Test Coverage
On an SM107 GPU, in a container whose CUDA toolkit is not under
/usr/local/cuda(no/usr/local/cudaat all), withCUDA_HOMEset,pytest tests/unittest/_torch/attention/test_attention_mla.py:Cannot parse NVCC versionerror above, reported in [Bug]: trtllm-gen FMHA JIT requires /usr/local/cuda/bin/nvcc (ignores CUDA_HOME / PATH) even with NVRTC, failing MLA generation and executor warmup when the toolkit lives elsewhere #20515).nvccerrors (the test file was taken from [#20506][fix] Size the generation-only attention workspace without the context requests #20520, which adds one test)CUDA_HOMEpointing at a directory whosebin/nvccis a stub that logs each call and forwards only--versionto the realnvcc: 96 passed, 8 skipped (that one test deselected), and the stub was called exactly once, as/stubhome/bin/nvcc --version. So the archive uses the emittednvccPath.The GPU build was main at e88d19c, whose C++ is identical to current main, with #20518 (needed on SM107) and the fixes for both #20506 and #20515 applied; the two touch unrelated code.
There is no unit test: the resolution is a few lines of environment lookup, and the effect is only visible through the archive's JIT, which the existing MLA tests above already exercise when the toolkit is elsewhere.
PR Checklist
Dev Engineer Review
The FMHA configuration resolves one executable
nvccper process fromCUDA_HOME,CUDA_PATH, thenPATH. It skips non-regular or non-executable candidates and emitsnvccPathonly when the path is JSON-safe. Otherwise, the archive default remains. Windows keeps the existing behavior.QA Engineer Review
No test changes.
Per-File QA Perspective
cpp/tensorrt_llm/kernels/trtllmGenKernels/fmha/fmhaKernels.h: Verify environment precedence, executable checks, process-wide caching,PATHparsing, JSON-safe path filtering, and fallback behavior when no candidate is found. Verify the existing Windows behavior.