[BugFix] Fix returned logprobs with spec decode + prefill chunking#29216
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DarkLight1337 merged 1 commit intovllm-project:mainfrom Nov 22, 2025
Merged
[BugFix] Fix returned logprobs with spec decode + prefill chunking#29216DarkLight1337 merged 1 commit intovllm-project:mainfrom
DarkLight1337 merged 1 commit intovllm-project:mainfrom
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Also: - Fix error with bf16 models and "raw_logits" mode - Use smaller model for test Signed-off-by: Nick Hill <nhill@redhat.com>
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This pull request addresses a bug where logprobs were incorrectly calculated during speculative decoding with prefill chunking. The main fix in vllm/v1/worker/gpu_model_runner.py correctly computes token offsets for logprobs before any tokens are discarded, which resolves the issue. Additionally, the PR includes a fix for handling bfloat16 models in raw_logits mode and updates the relevant test to use a smaller model and reliably trigger the chunking behavior. The changes are well-implemented and the logic is sound. I approve of this pull request.
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Yes, this works, thanks for fixing @njhill ! |
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The produced logprobs lists in this case were incorrect due incorrectly taking into account sampled token "discards" when computing offsets into the logprobs tensors.
Also:
Original PR which had this mistake: #26060
cc @TheEpicDolphin