[Metrics] Scope unregister_vllm_metrics() to strictly "vllm:" metrics

[vraiti]

Purpose

unregister_vllm_metrics() currently uses "vllm" in collector._name to decide which collectors to remove from the Prometheus registry. This is a substring match that removes every collector whose internal name contains vllm anywhere, including metrics registered by other subsystems or downstream extensions that happen to use vllm in their metric names.

This came up when trying to add Prometheus support to vLLM-Omni: vllm-project/vllm-omni#3362 (comment)

Since the architecture of vLLM-Omni requires that multiple Prometheus collectors be maintained, unregister_vllm_metrics() requires that we use some sort of workaround to preserve our own metrics without messing with the internals of vLLM's metrics. The simpler solution IMO would be for vLLM to just be specific about which metrics it wants to ensure are uninitalized when PrometheusStatLogger is instantiated.

This PR solves this by updating the startwisth string match in unregister_vllm_metrics from "vllm" to "vllm:", meaning that "vllm_omni:"

Changes

• vllm/v1/metrics/prometheus.py: change startswith("vllm") to startwith("vllm:")

Test Plan

Deploy vLLM-Omni with patched vLLM

Test Result

No errors

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[claude]

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[gemini-code-assist]

Code Review

This pull request introduces a more granular approach to unregistering vLLM metrics by maintaining an explicit list of metric names in _STAT_LOGGER_METRIC_NAMES. This change ensures that only metrics owned by the PrometheusStatLogger are removed, leaving metrics from other subsystems intact. Additionally, a new test is added to verify that this list stays synchronized with the source code. Review feedback suggests improving the test's regular expression to be more robust against different string formatting and refactoring a line continuation to follow PEP 8 guidelines.

[markmc]

unregister_vllm_metrics() currently uses "vllm" in collector._name to decide which collectors to remove from the Prometheus registry. This is a substring match that removes every collector whose internal name contains vllm anywhere, including metrics registered by other subsystems or downstream extensions that happen to use vllm in their metric names.

This came up when trying to add Prometheus support to vLLM-Omni: vllm-project/vllm-omni#3362 (comment)

How about:

• Change the check to collector._name.startswith("vllm:")
• Change vllm:omni_ to vllm_omni:

[vraiti]

How about:

• Change the check to collector._name.startswith("vllm:")
• Change vllm:omni_ to vllm_omni:

@wuhang2014 what do you think?

[wuhang2014]

How about:

• Change the check to collector._name.startswith("vllm:")
• Change vllm:omni_ to vllm_omni:

@wuhang2014 what do you think?

One concern is that for models like qwen3-omni, which have two LLM stages, this would initialize the collector twice.

[vraiti]

One concern is that for models like qwen3-omni, which have two LLM stages, this would initialize the collector twice.

Under vLLM-Omni's current architecture and the design of vLLM-Omni/#3362, it would not. The collector is initialized once in the orchestrator and collects all vLLM metrics from any LLM-type stages.

[wuhang2014]

One concern is that for models like qwen3-omni, which have two LLM stages, this would initialize the collector twice.

Under vLLM-Omni's current architecture and the design of vLLM-Omni/#3362, it would not. The collector is initialized once in the orchestrator and collects all vLLM metrics from any LLM-type stages.

I'm good with it then.

[vraiti]

@markmc we should be good with just a simple startswith("vllm:") :)

[mergify]

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[vraiti]

@markmc The CI seems to be failing just due to the fact that the runners are not being allocated GPUs. Is there a way to get around this?

[mergify]

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

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.