[bench] Fix benchmark/serve.py to ignore unavailable results

[lk-chen]

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)".
• The test plan, such as providing test command.
• 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

FIX #22381

Test Plan

vllm serve Qwen/Qwen2.5-0.5B

vllm bench serve \
    --model Qwen/Qwen2.5-0.5B \
    --percentile-metrics ttft,tpot \
    --save-results

Test Result

(Optional) Documentation Update

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[gemini-code-assist]

Code Review

This pull request fixes an issue in benchmark/serve.py where saving benchmark results could fail with a KeyError if a metric was not present in the results. The fix correctly adds a check to ensure metrics exist before trying to access them. My review identifies a small area for improvement where a redundant check was added in the extra_info dictionary comprehension. I've suggested removing this redundant check to improve code clarity and maintainability.

[gemini-code-assist]

The check k in results is redundant here. The dictionary comprehension already iterates over the keys of the results dictionary with for k in results, so k is guaranteed to be in results. You can simplify this condition to improve code clarity.

            for k in results if k not in metrics and k not in ignored_metrics

[lk-chen]

fixed