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[Tests] Update online DP tests to verify that requests are balanced #20157

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merged 5 commits into from
Jul 3, 2025

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@njhill njhill commented Jun 27, 2025

This was a gap in our current DP tests.

Updated to use metrics to verify that requests are balanced evenly between the data parallel ranks.

Via custom stats logger in the AsyncLLM interface case and external prometheus metrics in API server case.

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Summary of Changes

Hello @njhill, 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 enhances the testing suite for data parallel (DP) configurations by introducing comprehensive checks to ensure that incoming requests are effectively balanced across different data parallel ranks. It addresses a previously identified gap in test coverage by leveraging both internal custom statistics logging for the AsyncLLM interface and external Prometheus metrics for the API server, providing robust verification of request distribution.

Highlights

  • Enhanced Data Parallel Tests: New tests and modifications are introduced to verify that requests are balanced evenly across data parallel ranks in both AsyncLLM and API server contexts, addressing a previous gap in test coverage.
  • Prometheus Metrics Integration: For API server tests, new utility functions (get_prometheus_metrics, get_engine_request_counts) are added to fetch and parse Prometheus metrics, specifically vllm:request_success_total, to determine request distribution per engine.
  • Custom Stats Logger for AsyncLLM: A SimpleStatsLogger is implemented and integrated into AsyncLLM tests to track and verify request completion counts per engine, ensuring proper balancing within the internal engine.
  • Request Balancing Assertions: Assertions are added to both API server and AsyncLLM tests to confirm that all data parallel engines receive requests and that the distribution of these requests is reasonably balanced.
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@mergify mergify bot added the v1 label Jun 27, 2025
@@ -38,7 +38,7 @@ def default_server_args():
]])
def server(default_server_args, request):
if request.param:
default_server_args.extend(request.param)
default_server_args = default_server_args + request.param
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Small unrelated test fix

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Code Review

This pull request adds tests to verify that requests are balanced across data parallel ranks, which is a great addition for ensuring the correctness of the DP implementation. The approach of using Prometheus metrics for the API server and a custom stats logger for the AsyncLLM interface is sound. The code is generally well-written. I've provided a few suggestions to improve the robustness and maintainability of the new test code.

njhill added 4 commits July 1, 2025 17:48
Signed-off-by: Nick Hill <[email protected]>
Signed-off-by: Nick Hill <[email protected]>
Signed-off-by: Nick Hill <[email protected]>
@njhill njhill force-pushed the dp-and-api-tests branch from d7338f8 to 2f9894f Compare July 1, 2025 16:48
@njhill njhill added the ready ONLY add when PR is ready to merge/full CI is needed label Jul 1, 2025
Signed-off-by: Nick Hill <[email protected]>
@vllm-project vllm-project deleted a comment from gemini-code-assist bot Jul 2, 2025
@DarkLight1337 DarkLight1337 merged commit 67d25ec into vllm-project:main Jul 3, 2025
51 of 52 checks passed
@njhill njhill deleted the dp-and-api-tests branch July 3, 2025 06:53
sfeng33 pushed a commit to sfeng33/vllm that referenced this pull request Jul 6, 2025
huydhn pushed a commit to huydhn/vllm that referenced this pull request Jul 8, 2025
LyrisZhong pushed a commit to LyrisZhong/vllm that referenced this pull request Jul 23, 2025
avigny pushed a commit to avigny/vllm that referenced this pull request Jul 31, 2025
Pradyun92 pushed a commit to Pradyun92/vllm that referenced this pull request Aug 6, 2025
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