perf_hooks: add options to monitorEventLoopDelay() by jasnell · Pull Request #66115 · nodejs/node

jasnell · 2026-09-18T19:40:17Z

Adds options to tune histogram parameters to monitorEventLoopDelay()

Also fix a truncation and doc bug.

codecov · 2026-09-18T21:25:09Z

Codecov Report

❌ Patch coverage is 85.71429% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.37%. Comparing base (9c06dab) to head (0e5e587).
⚠️ Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_perf.cc	58.82%	0 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66115      +/-   ##
==========================================
- Coverage   90.37%   90.37%   -0.01%     
==========================================
  Files         790      792       +2     
  Lines      274272   275340    +1068     
  Branches    52502    52769     +267     
==========================================
+ Hits       247865   248830     +965     
- Misses      16890    16924      +34     
- Partials     9517     9586      +69

Files with missing lines	Coverage Δ
lib/internal/histogram.js	`97.52% <100.00%> (+<0.01%)`	⬆️
lib/internal/perf/event_loop_delay.js	`95.90% <100.00%> (+1.00%)`	⬆️
src/histogram.cc	`86.67% <100.00%> (-0.14%)`	⬇️
src/histogram.h	`84.31% <ø> (ø)`
src/node_perf.cc	`86.11% <58.82%> (-1.85%)`	⬇️

... and 61 files with indirect coverage changes

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`IntervalHistogram` stored the interval as `int32_t`, so a resolution above 2^31 - 1 ms wrapped: `resolution: 2 ** 32 + 1` sampled every millisecond. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode

It counts values above the highest recordable value, for every histogram type. Event loop delay histograms no longer have a 1 hour limit. Signed-off-by: James M Snell <jasnell@gmail.com> Refs: nodejs#41153 Assisted-by: OpenCode

Accept `lowest`, `highest`, and `figures`, as `createHistogram()` does. The defaults are unchanged, and use up to 432 KiB per histogram. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode

mcollina

lgtm

(linting is failing)

nodejs-github-bot · 2026-09-26T12:38:02Z

CI: https://ci.nodejs.org/job/node-test-pull-request/77956/

Co-authored-by: Filip Skokan <panva.ip@gmail.com>

nodejs-github-bot · 2026-09-26T21:31:23Z

CI: https://ci.nodejs.org/job/node-test-pull-request/77979/

nodejs-github-bot · 2026-09-27T06:55:26Z

CI: https://ci.nodejs.org/job/node-test-pull-request/77994/

nodejs-github-bot · 2026-09-27T08:10:18Z

Landed in 2ce7a73

`IntervalHistogram` stored the interval as `int32_t`, so a resolution above 2^31 - 1 ms wrapped: `resolution: 2 ** 32 + 1` sampled every millisecond. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode PR-URL: nodejs#66115 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Filip Skokan <panva.ip@gmail.com>

`IntervalHistogram` stored the interval as `int32_t`, so a resolution above 2^31 - 1 ms wrapped: `resolution: 2 ** 32 + 1` sampled every millisecond. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode PR-URL: #66115 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Filip Skokan <panva.ip@gmail.com>

jasnell added semver-minor PRs that contain new features and should be released in the next minor version. perf_hooks Issues and PRs related to the perf_hooks module and performance measurement APIs. labels Sep 18, 2026

jasnell requested review from ShogunPanda and mcollina September 18, 2026 19:40

nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. lib / src Issues and PRs involving general changes in the lib/ or src/ directories. needs-ci PRs that need a full CI run. labels Sep 18, 2026

jasnell added 3 commits September 25, 2026 23:33

perf_hooks: fix truncation of monitorEventLoopDelay() resolution

692a3a8

`IntervalHistogram` stored the interval as `int32_t`, so a resolution above 2^31 - 1 ms wrapped: `resolution: 2 ** 32 + 1` sampled every millisecond. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode

doc: fix description of histogram.exceeds

468ca5c

It counts values above the highest recordable value, for every histogram type. Event loop delay histograms no longer have a 1 hour limit. Signed-off-by: James M Snell <jasnell@gmail.com> Refs: nodejs#41153 Assisted-by: OpenCode

perf_hooks: add range options to monitorEventLoopDelay()

4fee958

Accept `lowest`, `highest`, and `figures`, as `createHistogram()` does. The defaults are unchanged, and use up to 432 KiB per histogram. Signed-off-by: James M Snell <jasnell@gmail.com> Assisted-by: OpenCode

jasnell force-pushed the jasnell/perf-hooks-eld-range-options branch from ca68db9 to 4fee958 Compare September 25, 2026 23:35

jasnell requested a review from trivikr September 25, 2026 23:36

mcollina approved these changes Sep 26, 2026

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Comment thread test/parallel/test-perf-hooks-monitor-event-loop-delay-options.js Outdated

Comment thread doc/api/perf_hooks.md Outdated

Apply batched suggestions from code review

0e5e587

Co-authored-by: Filip Skokan <panva.ip@gmail.com>

jasnell added commit-queue-squash PRs the Commit Queue should land as one squashed commit. and removed commit-queue-rebase PRs the Commit Queue should land as multiple self-contained commits. labels Sep 26, 2026

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nodejs-github-bot merged commit 2ce7a73 into nodejs:main Sep 27, 2026
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perf_hooks: add options to monitorEventLoopDelay() - #66115

perf_hooks: add options to monitorEventLoopDelay()#66115
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