[Feature] use --eplb_config to set eplb param

[lengrongfu]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)". [Feature] Expert Parallelism Load Balancer (EPLB) #18343 (comment)
• The test plan, such as providing test command.

$ vllm -m vllm.entrypoints.cli.main serve .....  --eplb-config \{\"enable_eplb\":True\}

• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

Purpose

Test Plan

Test Result

(Optional) Documentation Update

[github-actions]

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[gemini-code-assist]

Summary of Changes

Hello @lengrongfu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly refactors how Expert Parallelism Load Balancing (EPLB) parameters are managed and passed within the vLLM system. The core change involves introducing a dedicated EPConfig dataclass to encapsulate all EPLB-related settings, moving away from disparate individual parameters. This not only improves the internal organization of the configuration but also streamlines the command-line interface by consolidating multiple arguments into a single, JSON-configurable --ep-config option. The necessary code adaptations have been made across the project to utilize this new, more structured approach.

Highlights

• Configuration Refactoring: All Expert Parallelism Load Balancing (EPLB) related parameters have been consolidated into a new EPConfig dataclass. This centralizes the configuration for features like enable_eplb, lb_window_size, lb_step_interval, and lb_log_balancedness.
• Simplified CLI Interface: The multiple individual command-line arguments for EPLB parameters (e.g., --enable-eplb, --eplb-window-size) have been replaced with a single --ep-config argument. This new argument accepts a JSON string, allowing for more flexible and structured configuration directly from the CLI.
• Codebase Adaptation: Various parts of the vLLM codebase, including ParallelConfig, EngineArgs, eplb_state.py, deepseek_v2.py, and gpu_model_runner.py, have been updated to reflect the new nested ep_config structure, ensuring seamless integration and continued functionality.

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[gemini-code-assist]

Code Review

This pull request is a great step towards better code organization by refactoring the EPLB parameters into a dedicated EPConfig dataclass. The implementation is clean and consistent across the codebase. I've identified one critical issue with the programmatic initialization of ep_config that would cause a runtime failure. The fix is straightforward and included in my comment. Once that's addressed, this PR will be in excellent shape.

[simon-mo]

@abmfy please review when you get the chance, thanks!

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @lengrongfu.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[hmellor]

I've not left a full review but I have a few questions/suggestions.

The main question is why not add more fields to ParallelConfig?

[lengrongfu]

I've not left a full review but I have a few questions/suggestions.

The main question is why not add more fields to ParallelConfig?

This is a good suggestion, and it would be better to implement it in ParallelConfig.

[lengrongfu]

@hmellor please take a look, will done modify based on suggest.

[abmfy]

Hi @lengrongfu, thank you again for your contribution! Just wanted to check in on the update for this doc:

Thank you for your contribution! As a final step, could you please update the corresponding documentation at expert_parallel_deployment.md? This will help users migrate smoothly to the new CLI interface.

[lengrongfu]

Hi @lengrongfu, thank you again for your contribution! Just wanted to check in on the update for this doc:

Thank you for your contribution! As a final step, could you please update the corresponding documentation at expert_parallel_deployment.md? This will help users migrate smoothly to the new CLI interface.

I will commit a pr in today. thanks tips ~