[Metrics] Scope unregister_vllm_metrics() to PrometheusStatLogger-owned 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 replaces the substring match in unregister_vllm_metrics with a check against a frozenset of the 66 metric names that vLLM defines throughout its codebase. Only those collectors are unregistered before re-creation.

This makes it safe for downstream projects (e.g. vLLM-Omni) to use PrometheusStatLogger while registering their own vllm:-prefixed metrics.

To ensure that there is not drift between the metrics that vLLM actually uses and the metrics listed in the frozenset, this PR also adds a small new CI test that performs the one-to-one check between _STAT_LOGGER_METRIC_NAMES and the vLLM codebase.

Changes

• vllm/v1/metrics/prometheus.py: Add _STAT_LOGGER_METRIC_NAMES frozenset containing all 66 metric names defined in the codebase. Update unregister_vllm_metrics() to filter by set membership instead of substring match.
• tests/v1/metrics/test_metric_name_registry.py (new): CI test that extracts all name="vllm:..." literals from the owned source files and asserts a one-to-one mapping with the frozenset. Catches both missing entries (would cause ValueError: Duplicated timeseries on second instantiation) and stale entries (dead weight).

Test Plan

python -m pytest tests/v1/metrics/test_metric_name_registry.py -v

Test Result

tests/v1/metrics/test_metric_name_registry.py::test_stat_logger_metric_names_match_source PASSED
tests/v1/metrics/test_metric_name_registry.py::test_owned_source_files_exist PASSED

2 passed in 3.68s

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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]

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

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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?