Negative utilization in eventLoopUtilization for worker_threads

[tshemsedinov]

Version

v14.18.1, v15.14.0, v16.11.1, v17.0.0-pre (as of 16 Oct `21)

Platform

Linux marcus 5.13.19-200.fc34.x86_64 #1 SMP Sat Sep 18 16:32:24 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

worker_threads

What steps will reproduce the bug?

Repository with example: https://github.com/tshemsedinov/wtu

How often does it reproduce? Is there a required condition?

If worker event loop is empty in delta calculation period.

What is the expected behavior?

Delta fields active and utilization are expected to be positive, utilization expected to be [0..1].

What do you see instead?

Negative values in ~50% cases. But if you add setInterval with empty handler for minimum eventloop load, utilization will be always between 0 and 1.

Additional information

I know that it is a stable API but it would be better in far future:

• I'd propose to reduce time between loopIdleTime() call and now() in lower level, but my experiments in this field is not successful, still getting negative utilization.
• To decompose this function to respect separation of concerns into performance.eventLoopUsage(): EventLoopUsage and performance.eventLoopUtilization(usage1, usage2): EventLoopUtilization.
• Now we have 6 places to calculate proportion (for utilization), 3 in internal/worker.js and 3 in internal/perf/event_loop_utilization.js.

[tshemsedinov]

Refs: #35664
Refs: #37134

FYI: @trevnorris and @addaleax

[trevnorris]

Thanks. I'll give it a look.