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[Bugfix]Fix FlashInfer warmup crash: autotune(tuning_buckets=...) must round M up, not down (Invalid MXFP8 split-K tactic with spec-decode) - #58165
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| # time. The autotuner's override default is floor mapping, which hands a | ||
| # cute-dsl low-M split-K tactic tuned at bucket b to calls with | ||
| # b < M < next bucket; the runner then rejects the tactic (its MMA tile | ||
| # is chosen by rounding M up) and the dummy run raises |
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Could we keep this comment shorter? I think just 1-2 lines explaining why round_up=True is needed should be enough.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Yongye Zhu <zyy1102000@gmail.com>
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Yongye Zhu <zyy1102000@gmail.com>
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The drafter runs inside the same dummy run as the target model but with up to num_draft_reqs * num_query_per_req tokens, which can exceed the pass's num_tokens (e.g. the bounded deferred-MoE pass). Buckets built from num_tokens alone then clamp the drafter's M to a smaller bucket and replay tactics that are invalid for it, crashing warmup with dspark. Build the buckets from the larger of the two. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Yongye Zhu <zyy1102000@gmail.com>
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Resolves the conflict with vllm-project#58165 in kernel_warmup.py: keeps main's round_up=True on the FlashInfer autotune context and this PR's capture of the dummy run output used for the nvfp4_dynamic logits autotune. Signed-off-by: Stefano Castagnetta <scastagnetta@nvidia.com>
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…t round M up, not down (Invalid MXFP8 split-K tactic with spec-decode) (vllm-project#58165) Signed-off-by: Yongye Zhu <zyy1102000@gmail.com> Co-authored-by: Yongye Zhu <zyy1102000@gmail.com> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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Fix FlashInfer warmup crash:
autotune(tuning_buckets=...)must map runtime M up, not downFixes the engine crash-loop at startup for SM100/SM103 block-scaled cute-dsl linear kernels (
mm_mxfp8/mm_fp4) when speculative decoding is enabled.The crash
kernel_warmupruns dummy forwards insidefi_utils.autotune(tuning_buckets=tuning_buckets). With spec-decode, the DSpark draft model forward runs at M =max_num_seqs × k= e.g. 8 × 3 = 24 — not a bucket value. Boot dies:at
flashinfer/gemm/gemm_base.py:5327(CuteDSLMxfp8GemmRunner.forward), reached from the draft model'sfused_wqa_wkvGEMM.Reproduced on DGX Station GB300 (SM103) with vLLM nightly + DeepSeek-V4.1-Flash + dspark k=3; standalone FlashInfer-only repro at flashinfer-ai/flashinfer#5450.
Root cause
mm_mxfp8's own tuning config maps runtime M to buckets withmap_to_hybrid_bucket_uncapped, which rounds up, and the cute-dsl split-K MMA tile is likewise chosen by rounding M up (mma_tiler_mn_for_m: 8/16/32). A tactic tuned at bucket b is therefore valid for every M ≤ b — tune space and apply space agree.But inside
autotune(tuning_buckets=...)the autotuner replaces the op's mapper withmake_bucket_mapper(buckets, round_map=round_up)andround_updefaults to False (floor). So the warmup dummy run at M=24 looks up the bucket-16 tactic — tile (128,16), split_k=4 — andforward()rejects it becausemma_tiler_mn_for_m(24)is (128,32).Outside the context (serving, CUDA-graph capture) the op's own round-up mapper is restored, so only the warmup pass ever crashes: the engine can never boot, while the identical weights, tactics, and cache would serve fine.
Standalone repro (no vLLM, one process, same cache — all three regimes):
The fix
One line:
round_up=Trueon the warmupautotune()call, making tune-context mapping equal serving-time mapping. Every cached tactic at bucket b is then applied only to M ≤ b — exactly the envelope both the split-K validator and the small swap-AB base tactics guarantee.Profiling is per bucket, so tactic choices and the cache file are unchanged; only the dummy run's execution path changes. Verified live on GB300: the crash-looping boot (identical config) boots clean with this change and serves with full CUDA graphs; warmup passes on the pre-existing cache.
Broader hazard (why this should land even before any FlashInfer-side change)
The base (non-split-K) candidate tactics include swap-AB tiles (128, 8/16/32) whose persistent-kernel
can_implementrequireskernel_n ≤ tile_n(kernel_n = token count in swap-AB) — and those tactics get no apply-time check. Under floor mapping, a bucket-16 winner applied at M=24 runs silently outside its envelope. The same tactic generator servesmm_fp4, so NVFP4 + spec-decode is exposed too. The split-KValueErroris just the one place that notices. Filed upstream with full analysis: flashinfer-ai/flashinfer#5450Notes for reviewers
DynamicDim.max), this line remains a correct, self-contained fix on the vLLM side and can be revisited later.