[PD-Disagg][Fix] Remove 'test_external_dp_routing' from Rust Router constructor parameters.

[Duyi-Wang]

cc @hnyls2002

Motivation

test_external_dp_routing param has been introduced in #19268 for minilb test and was not filtered out when transmitted to the Rust implementation. The error occured.

python -m sglang_router.launch_router --pd-disaggregation --port 30000 --policy random --prefill-policy random --decode-policy random --prefill http://10.235.192.132:8000 --decode http://10.235.192.132:8000
Both --prefill-policy and --decode-policy are specified. The main --policy flag will be ignored for PD mode.
Error starting router: Router.__new__() got an unexpected keyword argument 'test_external_dp_routing'
Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/opt/venv/lib/python3.10/site-packages/sglang_router/launch_router.py", line 109, in <module>
    main()
  File "/opt/venv/lib/python3.10/site-packages/sglang_router/launch_router.py", line 105, in main
    launch_router(router_args)
  File "/opt/venv/lib/python3.10/site-packages/sglang_router/launch_router.py", line 52, in launch_router
    raise e
  File "/opt/venv/lib/python3.10/site-packages/sglang_router/launch_router.py", line 47, in launch_router
    router = Router.from_args(router_args)
  File "/opt/venv/lib/python3.10/site-packages/sglang_router/router.py", line 312, in from_args
    return Router(_Router(**args_dict))
TypeError: Router.__new__() got an unexpected keyword argument 'test_external_dp_routing'

Modifications

Add it to filter list.

Accuracy Tests

GSM8K test with 1P/1D of DeepSeek R1 TP8

/sgl-workspace/sglang/benchmark/gsm8k# python bench_sglang.py --num-questions 200 --port 8000
Downloading from https://raw.githubusercontent.com/openai/grade-school-math/master/grade_school_math/data/test.jsonl to /tmp/test.jsonl
/tmp/test.jsonl: 732kB [00:00, 20.4MB/s]                                                           
100%|████████████████████████████████████████████████████████████| 200/200 [00:16<00:00, 12.48it/s]
Accuracy: 0.970
Invalid: 0.000
Latency: 16.031 s
Output throughput: 1129.922 token/s

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.

Review Process

1. Ping Merge Oncalls to start the PR flow. See the PR Merge Process.
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   • /tag-run-ci-label, /rerun-failed-ci, /tag-and-rerun-ci
4. After green CI and required approvals, ask Merge Oncalls to merge.

[gemini-code-assist]

Summary of Changes

Hello, 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 addresses a runtime error during the router's initialization by preventing a Python-specific test argument from being incorrectly forwarded to the underlying Rust implementation. This ensures the router starts without encountering unexpected keyword argument errors, improving stability and correct argument handling.

Highlights

• Bug Fix: Resolved a TypeError that occurred when the test_external_dp_routing parameter was unexpectedly passed to the Rust Router constructor, by adding it to the argument filtering list.

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Changelog

• sgl-model-gateway/bindings/python/src/sglang_router/router.py
  • Added test_external_dp_routing to the list of arguments that are filtered out before being passed to the Rust Router constructor.

Activity

• Initial review requested by Duyi-Wang, with cc @hnyls2002.
• Accuracy tests for GSM8K were performed and passed, indicating no regression in model outputs.

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[gemini-code-assist]

Code Review

This pull request correctly addresses a TypeError by filtering out the test_external_dp_routing parameter before it's passed to the Rust Router constructor. This resolves the crash described. I've included one suggestion to also filter out shutdown_grace_period_secs, which appears to be another parameter from RouterArgs not handled by the Rust implementation, to prevent a similar issue in the future.