vllm
[Frontend][Core] Move logits processor construction to engine
#7666
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[Frontend][Core] Move logits processor construction to engine #7666

joerunde wants to merge 1 commit into vllm-project:main from joerunde:backend-logits
joerunde
joerunde274 days ago

Followup for #6797

This PR moves the logits processor construction out of the frontend api server, instead passing through the relevant request parameters so that the LLMEngine can construct our standard set of logits processors. This does not remove the logits_processors parameter from SamplingParams to maintain compatibility for other use cases besides the OpenAI frontend where users may be passing in their own logits processors.

The goal here is to

  • remove the need to pickle up the logits processors to send over ZMQ, which should improve performance
  • simplify the UX so all consumers of the LLMEngine api who are using our logits processors now no longer need to construct them and pass them in

I still need to do some profiling and look at all the tests. I may have to end up putting back an async method for constructing these logits processors that can run in a separate thread in the engine, I think as-is compiling a hefty FSM might block up the gpu event loop.


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joerunde :alembic: move logits processor construction to engine
66591952
github-actions
github-actions274 days ago

👋 Hi! Thank you for contributing to the vLLM project.
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Once the PR is approved and ready to go, please make sure to run full CI as it is required to merge (or just use auto-merge).

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njhill
njhill commented on 2024-08-20
njhill274 days ago

Thanks @joerunde! I haven't had a chance to look in detail yet but have a couple of initial comments:

  • I agree we should check that these changes don't result in any worse overhead from LP construction due to different thread blocking behaviour for example
  • Not sure whether you looked at #6878 which was added recently, but I guess it would make sense to reconcile those changes as part of this. If we're adding new params into SamplingParams then we should probably deprecate/remove the new LLM guided_options_request arg which was added there
vllm/sampling_params.py
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41@dataclass
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class LogitsProcessorParams:
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"""Parameters required to construct one or more logits processors"""
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logit_bias: Optional[Union[Dict[int, float], Dict[str, float]]]
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allowed_token_ids: Optional[List[int]]
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guided_decoding_request: Optional[ # type: ignore
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'GuidedDecodingRequest'] # noqa
njhill274 days ago

I think these should probably just be top-level sampling params, the fact that these get turned into logits processors is a bit of an implementation detail.

joerunde
joerunde273 days ago

Thanks @joerunde! I haven't had a chance to look in detail yet but have a couple of initial comments:

  • I agree we should check that these changes don't result in any worse overhead from LP construction due to different thread blocking behaviour for example
  • Not sure whether you looked at Support for guided decoding for offline LLM #6878 which was added recently, but I guess it would make sense to reconcile those changes as part of this. If we're adding new params into SamplingParams then we should probably deprecate/remove the new LLM guided_options_request arg which was added there

Ah shoot, yeah I just saw those in the conflicts, not sure how those didn't end up here when I started this :(

I could go either way on adding these to sampling params or using a guided_options_request or logits_processor_request, maybe I'll go ask in slack for opinions

joerunde
joerunde256 days ago

closing for #8252

joerunde joerunde closed this 256 days ago

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