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[Bugfix][V0] Multi-sequence logprobs streaming edge case #15259

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merged 2 commits into from
Mar 22, 2025

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andylolu2
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@andylolu2 andylolu2 commented Mar 21, 2025

There's a bug when using logprobs with multi-sequence with RequestOutputKind.DELTA. When a sequence finishes before the others, it's output_token_ids on the subsequent steps will be an empty array, until every sequence finishes. This cases an [-0:] slice into the logprobs array, which returns the entire logprobs array instead of the 0-length suffix.

Adding an if check to handle this edge case.

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@andylolu2 andylolu2 changed the title Handle multi-sequence logprobs edge case [Bugfix] Handle multi-sequence logprobs edge case Mar 21, 2025
@andylolu2 andylolu2 changed the title [Bugfix] Handle multi-sequence logprobs edge case [Bugfix] Multi-sequence logprobs streaming edge case Mar 21, 2025
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Thanks for the fix @andylolu2!

BTW this is on the v0 path which we're aiming to deprecate soon anyhow. Hopefully it's not an issue in v1.

@njhill njhill changed the title [Bugfix] Multi-sequence logprobs streaming edge case [Bugfix][V0] Multi-sequence logprobs streaming edge case Mar 21, 2025
andylolu2 and others added 2 commits March 21, 2025 20:04
Signed-off-by: Andy Lo <andy@mistral.ai>
Signed-off-by: Andy Lo <andy@mistral.ai>
@andylolu2 andylolu2 force-pushed the andy/fix-multiseq-logprobs branch from 80327d1 to 763405f Compare March 21, 2025 20:04
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Thanks @njhill! I've cleaned up the PR

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Thanks @andylolu2

@njhill njhill added the ready ONLY add when PR is ready to merge/full CI is needed label Mar 21, 2025
@vllm-bot vllm-bot merged commit df14302 into vllm-project:main Mar 22, 2025
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erictang000 pushed a commit to erictang000/vllm that referenced this pull request Mar 25, 2025
lengrongfu pushed a commit to lengrongfu/vllm that referenced this pull request Apr 2, 2025
lulmer pushed a commit to lulmer/vllm that referenced this pull request Apr 7, 2025
…t#15259)

Signed-off-by: Andy Lo <andy@mistral.ai>
Signed-off-by: Louis Ulmer <ulmerlouis@gmail.com>
nishith-fujitsu pushed a commit to nishith-fujitsu/vllm that referenced this pull request Apr 9, 2025
lk-chen pushed a commit to lk-chen/vllm that referenced this pull request Apr 29, 2025
shreyankg pushed a commit to shreyankg/vllm that referenced this pull request May 3, 2025
RichardoMrMu pushed a commit to RichardoMrMu/vllm that referenced this pull request May 12, 2025
…t#15259)

Signed-off-by: Andy Lo <andy@mistral.ai>
Signed-off-by: Mu Huai <tianbowen.tbw@antgroup.com>
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3 participants