[MoE/B12X] Auto-select direct B12X NVFP4 MoE before Marlin - #54669
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Prefer the optional SM12x-capable B12X backend before the Marlin fallback when its support predicate accepts the deployment. Add selector-order coverage and document automatic MoE selection. Related-to: vllm-project#49926 Related-to: vllm-project#50925 AI assistance from OpenAI Codex was used while developing this patch. The human submitter must review every changed line and is responsible for the contribution end-to-end. Co-authored-by: Codex <codex@openai.com> Signed-off-by: Nancy <nangld85@gmail.com>
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Documentation preview: https://vllm--54669.org.readthedocs.build/en/54669/ |
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Summary
Related issue: #54666
Related crash reports: #49926, #50925, #50934, #52225, #49070
Why this is not a duplicate
#47577 auto-selects the older FlashInfer B12X implementation on exact SM120 and deliberately excludes SM121. This change exposes the newer direct B12X backend merged in #52018. Its existing support predicate covers both SM120 and SM121 and remains the sole compatibility authority.
No open pull request found in the duplicate search adds
NvFp4MoeBackend.B12Xto the automatic NVFP4 MoE preference list.Verification performed
B12Xwhilemoe_backend='auto', completed piecewise and full CUDA-graph capture, warmed the B12X MoE signature, and returned HTTP 200 from/healthThe patch was rebased onto current
main; none of the three affected files changed between the tested base and the current base.Limits
The measurements do not identify the specific Marlin instruction responsible for the asynchronous illegal-memory-access fault, nor do they establish multi-day B12X stability. They show that a supported, merged backend is currently unreachable through automatic selection on this deployment while the Marlin fallback repeatedly faults.
AI-assistance disclosure
OpenAI Codex was used to develop, test, document, and prepare this change. This submission makes no claim of independent human line-by-line review; the full patch and evidence were first published for maintainer discussion in #54666.