[RFC] Remove/hook unused metrics #2901

[mdhaduk]

Opening this as a Draft PR

Changes

Removed unused metrics; used this script to generally identify which metrics might not be used, then manually removed them

To identify unused metrics, I used the following convention

For SharedIncMetric:

• Not incremented/added to
• Not stored
• Not fetched

For LatencyAggregateMetrics:

• Not calling record_latency_metrics

Metrics Removed:

• sync_response_fails
• sync_vmm_send_timeout_count
• deprecated_cmd_line_api_calls
• log_fails
• device_events
• rx_partial_writes
• tx_partial_reads

Reason

Resolving issue #2901 - Remove/hook unused metrics

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  how they are solving the problem in a clear and encompassing way.
• I have updated any relevant documentation (both in code and in the docs)
  in the PR.
• I have mentioned all user-facing changes in CHANGELOG.md.
• If a specific issue led to this PR, this PR closes the issue.
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• I have tested all new and changed functionalities in unit tests and/or
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• I have linked an issue to every new TODO.

---

• This functionality cannot be added in rust-vmm.

[roypat]

This is great, thanks for tackling this! I think we can probably even include your script in this PR (somewhere under tools) and then run it as part of our regular test suite, so we don't again reintroduce unneeded metrics later on :)

Btw, I think you can catch a few more unused ones with a tiny tweak to your script: Add metrics.rs files to the check that excludes specific use-sites. For example, the rx_partial_writes metric in net/metrics.rs is unused, but there's a .add call due to metrics aggregation inside the metrics files itself that makes your script believe it is in use.

[mdhaduk]

Great! Thank you for all the feedback, and I'm super stoked to potentially have my scripted integrated within the test suite!!

I went ahead and made the change to the script as you recommended which you can see above or here. Additionally, the following metrics may or may not be removed:

• metrics_count (SharedIncMetric)
• metrics_fails (SharedIncMetric)
• missed_metrics_count (SharedIncMetric)

I opted to ask you since removing them would require reworking src/metrics.rs and requests/metrics.rs; if you deem that is okay I will go ahead and make those changes as well!

Thanks!