[Frontend] Allow users to modify the scheduler configuration online in dev mode.

[noooop]

Purpose

Allow users to modify part of the scheduler configuration online, which will greatly simplify the benchmark process.

e.g.

vllm bench sweep only needs to be started once

cc @DarkLight1337 @lengrongfu

Test Plan

benchmark demo:
offline: https://github.com/noooop/snippet/blob/main/benchmarks/embed5/v1_offline.py
online: https://github.com/noooop/snippet/blob/main/benchmarks/embed5/v1_online.py

Test Result

nan

Known Issues

cudagraph_capture_sizes are different, the results will be slightly different.

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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[gemini-code-assist]

Code Review

The pull request introduces functionality to dynamically reconfigure scheduler parameters (max_num_seqs and max_num_batched_tokens) online. This is a valuable addition for benchmarking and dynamic resource management. The changes involve defining a SchedulerReconfigure data structure, adding reconfigure_scheduler methods across the engine components (LLM, EngineCoreClient, EngineCore), and implementing the reconfigure method in the Scheduler class. I've identified a critical bug in the fallback logic for max_num_batched_tokens and a high-severity design constraint regarding the modification limits.

[DarkLight1337]

Supporting this will introduce some constraints on the scheduler since it cannot assume that these parameters are constant anymore. That being said, I definitely see the value of being able to adjust the scheduling parameters on the fly as we don't have to restart the server each time the parameters change during benchmarking.

@WoosukKwon @njhill WDYT about this?

[mergify]

Hi @noooop, the pre-commit checks have failed. Please run:

uv pip install pre-commit
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

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Tip

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pre-commit run --hook-stage manual mypy-3.10
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[lengrongfu]

Could this parameter be designed to be more universal? If other parameters need to be modified in the future, there's no need to add new parameters. It's suggested to pass a structure or dic instead.

[noooop]

I also agree that passing a structure or dict would be better. Initially, the first version created a structure, but since there are only two parameters that can be modified, adding a structure just for that would make the code overly verbose. That’s why it was changed to the current approach.