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bench: pair nightly Criterion runs against the previous nightly - #6511
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Quest-Claim: 410d11cf09c88a2d
Each Rust bench group builds the previous scheduled Nightly's commit beside its own and runs both on one runner, alternating order. A quick screen flags slowdowns past 10%, alternating rounds confirm them, and a confirmed regression fails the job after its results upload, so the site publishes the comparison the alert links to. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
# Conflicts: # quest/m1/README.md
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Outcome: paired nightly comparison is implemented and pushed, and the PR stays a draft until the four decisions in the description are settled. Local validation: an A/A run flagged 3 of 31 kio cases in the screen and rejected all 3 in the rounds. A deliberately slowed (Written by Claude Opus 5.5) |
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughNightly Rust benchmark groups can compare the current commit with a selected base, defaulting to the previous scheduled Nightly. The runner screens benchmark cases and confirms selected slowdowns over alternating rounds. Comparison results include case verdicts and unavailable targets. The workflow gates successful paired runs, and reporting commands aggregate and publish paired data alongside nightly trends. The changes also add the Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to
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| Check name | Status | Explanation | Resolution |
|---|---|---|---|
| Docstring Coverage |  |
Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 54 functions across 8 files. | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Title check The title "bench: pair nightly Criterion runs against the previous nightly" matches the main change. The PR pairs each scheduled Nightly's Rust Criterion benchmarks with the previous scheduled Nightly… Description check The description explains the change in detail. It covers paired Criterion comparisons against the previous Nightly, the screen-and-confirm method, the regression gate, the site publishing of paired.js… Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Full details: Title check
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Explanation
The title "bench: pair nightly Criterion runs against the previous nightly" matches the main change. The PR pairs each scheduled Nightly's Rust Criterion benchmarks with the previous scheduled Nightly's commit, built and run on the same runner. The title is specific, concise, and follows a clear scope prefix. It omits the gate and the screen-and-confirm logic, which is acceptable.
Full details: Description check
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Explanation
The description explains the change in detail. It covers paired Criterion comparisons against the previous Nightly, the screen-and-confirm method, the regression gate, the site publishing of paired.json, the rust-bench/rust-shared split, the workflow inputs, and the validation runs. Every part relates to the changeset files, so the description is clearly on-topic.
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Actionable comments posted: 2
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Inline comments:
Review comments at @bench/compare.py:
- Around line 164-165: Validate the paired run’s round count in criterion_paired
and reject counts below three before evaluating cases, so insufficient samples
cannot be classified as noise and pass the gate.
- Around line 18-26: Update the paired-run agreement check in criterion_paired
to require every value in summarize’s paired_deltas_pct to be strictly positive,
in addition to the existing median threshold. A zero delta must not count as a
round that was slower.
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…cted packages A tied confirmation round no longer counts as slower, and the rule no longer depends on summarize's three-sample status, so any round count gates as documented. The base build keeps a --bench only when one of the selected packages has it, so a new target sharing another package's name reports as new instead of failing the whole base build. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Fetching a dispatched bench-base branch name only updates FETCH_HEAD, so the name never resolved in the shallow checkout. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Merging. Gates the nightly on paired benchmark regressions with the four recorded decisions, as the maintainer chose. CI is green, the current head has a non-Grok review, and (Written by Claude Opus 5.5) |
Each Nightly now compares every Rust Criterion bench against the previous scheduled Nightly's commit, built and run on the same hosted runner, and publishes the result beside the regression table. A confirmed regression fails the job, so the existing Alert workflow posts it to Discord.
Quest:
quest/m1/bench-ci.md. This PR rewrites it to what remains: calibrating the threshold with A/A and deliberately slowed runs, which needs maintainer-dispatched Nightly runs onmainafter this lands.How it works
bench/run.sh --criterionwithMOQ_BENCH_BASE=<rev>builds the selected targets withcargo bench --no-runin the checkout and in a base worktree (separate target dirs), then runs each target's executable from its package directory, the way cargo would. Each target runs once per side in the trend's quick mode, alternating which side goes first. The current side's estimates are still the trend point, so history is unchanged.bench/compare.py --criterion-screenflags cases more than 10% slower, worst first, at most 20 per group. Each one reruns in three alternating rounds (MOQ_BENCH_RUNTIME_ROUNDS) using the existing BASE comparison settings (1 s warmup, 2 s measurement, 30 samples). It counts as a regression only if every round is strictly slower and the median is above 10%, at any round count. Everything else gets classified asfaster,noise,unconfirmed(over the confirmation budget),unchanged,neworremoved. The result goes to the run'spaired.json. The relay comparison's statistics are now a sharedsummarize()helper.--benchtarget none of the base's selected packages has yet is dropped from the base build and reported asnew. Any other base build or run failure marks the targetunavailable, which fails the gate. A comparison that can't run never passes silently.sh/gh/nightly.sh.MOQ_BENCH_BASE=previous-nightlyresolves to the newest other scheduled Nightly onmainthroughgh run list, fetches it into the shallow checkout if needed, and passes the base on as a commit SHA so a dispatched branch name resolves.just gh benchmark-report rustalso writes the group's combinedpaired.json.paired: true. They getMOQ_BENCH_BASE(or the newbench-basedispatch input; the run's own commit gives an A/A run) andactions: readfor the lookup.Fail on paired regressionsstep (just gh benchmark-report gate) runs after the artifact upload. The workload still succeeds, so tonight's history is recorded, and the site publishes the comparison before the alert fires.preparecollects each successful source'spaired.json.benchmark-publish finishtakes it and writesbench/paired.jsonon gh-pages. The table page shows a "Paired comparison" section above the trend:rust-benchsplits:rust-benchkeeps net, net-cpu, kio and gst, and the 16-target shared build moves to a newrust-sharedleg (bench-rust-shared).net-cpunow builds with--features fuzz, so it reuses net's build instead of rebuilding (about 2 min a side on the runner).Measured on Nightly 2026-10-22 (current side only):
rust-benchrust-extrarust-uringAll of this comes on top of about 11 min of dev shell setup. Estimated paired legs, assuming a cold base build:
rust-benchrust-sharedrust-extrarust-uringThe base build should mostly hit mbx, since last night's main build uploaded it, but mbx's per-invocation download budget (5 GiB, exhausted tonight by the shared build) limits that.
Why a screen plus confirmation rather than full paired runs? The two Rust groups alone have about 1,700 cases. Even the BASE comparison's shorter settings take 3 s per case per side, which is about 3 h. Quick mode screens everything in the time the trend already spends. Only the few flagged cases pay for alternating rounds, and a bimodal case (common on hosted runners) has to land on the slow mode in all three rounds to fail.
Public API and wire impact
None. Tooling only. New knobs:
MOQ_BENCH_BASEforjust gh criterionandjust gh nightlybench-baseNightly dispatch inputjust gh benchmark-report gatejust gh benchmark-publish finish DIRECTORY PAIRED(wasfinish DIRECTORY)--pairedforbenchmark-report indexChecks
python3 bench/compare.test.py,python3 sh/gh/nightly.test.py,python3 sh/gh/bench-report.test.pyjust gh check(actionlint, alert coverage, run-step lint)MOQ_BENCH_BASE=HEADonkiowaiter+channel, 31 cases, on a loaded shared workstation. The screen flagged 3; all 3 were rejected asnoiseby the rounds. Exit 0.waiter_cancel, compared against HEAD. Confirmedregressionat +47.4% (rounds +47.4%, +47.9%, +46.2%), andjust gh benchmark-report gateexited 1.tee. The build functions now write their own output file.main(2026-10-23): the three Python suites,just gh check,quest checkandjust checkrerun.sh/gh/nightly.test.pyfailstest_every_cargo_bench_target_runs_nightlyonmoq-relay's newhttp_authbench, which fails onmaintoo; moq-dev/moq#6480 adds it to the shared invocation, so whichever lands second moves that line intorust-shared.bench-basebranch name only reachedFETCH_HEAD; fixed in 4b13d54.just checkreran green, and a local paired run of-p kio --bench waiteragainst HEAD built both sides and reported1 unchanged.Decisions
Settled by the maintainer on 2026-10-23 and recorded in the calibration quest's Plan.
rust-bench.rust-sharedout, restarting therust/shared/*trend history (three nights lost).rust-benchpaired is estimated at more than 80 min unsplit.(Written by Claude Opus 5.5)
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