fix(xtest): test benchmark improvements on the faster tail - #625
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IMPROVED was decided by `ci_high < 1/threshold and p_adjusted > 1 - alpha`, reading the *slower* tail's Benjamini-Hochberg adjusted p-value backwards. BH never lowers a p-value, so adjusting the upper tail and then requiring the result to be large makes that clause easier to satisfy the more cells a run has: a multiplicity correction that manufactures improvements instead of suppressing false ones. The two tails are not exact complements under the discrete signed-rank null either, so even unadjusted the reversal was not the test it claimed to be. `PairedComparison` now carries `p_value_faster` from `wilcoxon(alternative="less")` alongside the existing upper tail, and `apply_multiplicity_control` BH-adjusts both tails independently within each of the same two families (gated, rest) into `p_adjusted_faster`. IMPROVED reads `ci_high < 1/threshold and p_faster < alpha`, the exact mirror of the REGRESSION clause. Controls and censored keys still enter no family and fall back to their own raw tails. Both new fields are emitted in the JSON artifact; it stays "schema": 1, since this is additive evidence only. Regression coverage: the two control-only tests are kept, and a censored control-only case is added -- a run holding nothing but an A/A cell whose RSS is pinned at the measurement floor must still report `nothing_measured`. The existing RSS-floor tests pair the control with a real cell, so they cannot see that failure: inverting `analyze`'s `control_keys.add` and its censoring `continue` leaves the censored key looking like a candidate comparison and the run reports a PASS headline having measured nothing. The partial-round test now also asserts both arms' vectors stayed the same length, which `n_rounds` alone cannot show. New `TestFasterTail` covers both tails on `compare`, the adjusted faster tail deciding IMPROVED, BH applying to it within its family, controls and censored keys entering neither family, and a hand-built pair where BH lifts a 0.94 slower tail past 1 - alpha and the old rule would have called it IMPROVED on weak lower-tail evidence. Deadline handling, complete-round recording and the configured minimum-round refusal were already correct on main and are unchanged. xtest/perf/README.md documents the two tails, the mirrored IMPROVED rule, the new JSON fields, and the ordering `analyze` depends on. The invariant list stays at 8.
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Navigate logical layers of code changes, visualize relationships, and explore their blast radius. 📝 WalkthroughWalkthroughThe benchmark now computes and reports separate slower- and faster-direction p-values, and uses the faster tail for improvement verdicts. Documentation adds seeded statistical simulations and generated SVG figures. A draft specification describes a staged extension to multi-build benchmarking. ChangesBenchmark statistics and reporting
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant compare
participant apply_multiplicity_control
participant _verdict_for
participant _comparison_dict
compare->>apply_multiplicity_control: slower- and faster-tail p-values
apply_multiplicity_control->>_verdict_for: adjusted tails and comparison
_verdict_for->>apply_multiplicity_control: finalized verdict
apply_multiplicity_control->>_comparison_dict: finalized comparison
_comparison_dict->>_comparison_dict: serialize faster-tail values
Suggested reviewers: Merge Risk: 🔵 Low · up to The current benchmark changes are mergeable, but clarify artifact identity before implementing the multi-build plan so distinct builds are not treated as one. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The revised benchmark rule uses evidence from the correct statistical direction, and the reviewed paths show no new security boundary. The required comparison field could affect direct callers outside the reviewed code. Retained concerns
Security review detailsSecurity Blast Radius
Trust Boundaries and Controls
Resilience and Maintainability Implications
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 64 functions across 8 files. (2 skipped: 2 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Why the old IMPROVED rule was wrong is hard to see from the diff -- it reads like an algebraic identity. Adds three figures to perf/README.md that make the failure legible, plus the generator behind them: - fig1, three regions: the verdict margins (1.15 / 0.87) against the point null at 1.0, where both Wilcoxon tests actually sit. The CI clause carries the margin; across 1200 simulated cells the raw p-clause never once bound. - fig2, the correction runs backwards: BH never lowers a p-value, so `p_adjusted > 1 - alpha` gets easier as a run grows. Mean false IMPROVED cells per run go 0.43 / 2.71 / 6.28 at 4 / 12 / 24 cells under the old rule, against a flat ~0.06 under the new one. - fig3, positivity: the log transform fixes scale but not skew. One-sided stalls drive the slower tail's size to 0.815 and the faster tail's to 0.000 while the median ratio moves only 1.00 -> 1.07 -- which is why requiring both clauses is load-bearing, not belt-and-braces. Figure data is frozen as module constants rather than simulated at render time, so a scipy release that shifted a tie correction cannot silently rewrite three committed SVGs into an unreviewable diff. `--verify` re-runs the Monte Carlo and reports a mismatch for a human to judge; `--check` byte-compares for drift. Documentation only: nothing in perf/docs/ is imported by the harness, no test collects it, and the emitted report artifacts are untouched.
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No simulated number moves: `make_figures --verify` still matches every frozen constant and `--check` finds the three committed SVGs byte-identical, so this touches only how the simulations are written. - `_pair()` replaces four open-coded log-normal arm pairs. - `SEED_FALSE_IMPROVED` was left stale by the rename to `simulate_improvement_p_clause`; it is now `SEED_P_CLAUSE`. - `verify.THRESHOLD` was a third copy of a gating constant, in the module whose whole job is to agree with the gate. It imports `stats.DEFAULT_THRESHOLD`. - `_stall_rejection`'s `both_arms` flag switched between two genuinely different experiments, and left the control call discarding two of three return values. Split into `simulate_stall_tails` (back to its original 3-tuple) and `simulate_stall_size`, the helper now taking explicit per-arm stall rates. - Dropped a dead format column in figure 3's text-row loop.
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X-Test Failure Report✅ js@main-v0.27.0 |
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Review comments at @spec/DSPX-4372-t1.md:
- Around line 144-145: Update both neutral-outcome rules in the preparation
specification to require matching artifact identities, including build settings,
before treating same-commit aliases as equivalent; alternatively, explicitly
require identical build settings for those aliases. Add a test showing that
same-commit aliases with different build settings are not collapsed and still
receive the required comparison.
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Note to the Reviewer
stats.pyandreport.pyfor the actual changes; which are exercised in the tests.perfnow has some fun chartsspecfolder is just there to break down feat(xtest): compare up to four benchmark arms in one run #621, itself a small part in a larger PR I vibe coded a few months ago to improve the benchmark workflow's functionality (to allow comparing multiple versions of the same SDK) and readability/usefulness of the reportsBelow is Claude's explanation, if you want more details.
What this does
Fixes a real statistical defect on
main, restores the regression coveragethat guards it, and documents the resulting decision rule with three generated
figures. Two-arm only — no multi-arm, no report changes, no CI changes.
The IMPROVED verdict was decided with an invalid test.
_verdict_forconcluded a candidate was faster when
p > 1 - alpha, wherepis theBH-adjusted upper-tail (slower) p-value. Benjamini–Hochberg controls small
p-values and generally pushes large ones toward 1, so that backwards test gets
easier as a run grows rather than safer. There was no faster-tail p-value
computed anywhere.
Now:
_one_sided_pbecomes_one_sided_ps, returning(slower, faster)fromwilcoxon(alternative="greater")andwilcoxon(alternative="less").PairedComparisoncarriesp_value_fasterandp_adjusted_faster.correction families (gated, rest).
ci_high < 1/threshold and p_faster < alpha— the mirrorimage of the REGRESSION clause, not a reversal of it.
Restored coverage
test_control_only_run_measured_nothing_about_the_candidateandtest_control_plus_candidate_counts_as_measuredare preserved here, plus a newcase they did not cover: a control-only run whose RSS is pinned at the
measurement floor must still report
nothing_measured.analyzeregisterscontrol keys before the metric-specific censoring
continuefor exactly thisreason; reorder those two statements and the new test fails, which is the point.
Documentation (second commit)
perf/README.mdgains three figures explaining the decision rule, plus themachinery to keep them honest:
docs/svgkit.py— just enough SVG to draw them. No tick algorithm, no domaininference, no text measurement; ticks are literals and gutters are hand-laid.
Colors emit as CSS variables so one geometry pass serves light and dark.
docs/verify.py— the Monte Carlo behind every number.docs/make_figures.py— renders from frozen constants, never from a livesimulation, so a scipy release that shifts a tie correction cannot silently
rewrite three committed SVGs.
--verifyre-runs the simulation and reportsmismatches;
--checkfails on figure drift.The figures cover where the three verdicts sit on the ratio axis, the
multiplicity correction running backwards (the defect this PR fixes), and what
the log transform does and does not fix about positive right-tailed timings.
Review corrections
Review flagged three claims in the docs as overstated. Each was reproduced,
confirmed, and corrected — the fixes are in the figures and the simulation, not
just the prose:
simulate_null_improvement_ciadded and pinned, so the masking is stated rather than impliedci_without_significancepins the counterexamplesimulate_stall_sizeadded and plotted as aboth arms stalledrowThe third correction strengthens the argument rather than weakening it:
signed-rank is not being invalidated by skew, it is correctly answering a
point-null question that is the wrong question for a gate. That is precisely
why the margin lives in the CI clause, which is the conjunction this PR relies
on.
Validation
uv run ruff check .,uv run ruff format .,uv run pyright— clean.make_figures --verify— every frozen constant matches a fresh simulation.make_figures --check— committed SVGs match the generator byte for byte.p_slower > 1 - alphafails
test_adjusted_slower_tail_is_not_read_as_evidence_of_improvement(adjusted p 0.99 on a case whose true faster-tail p is 0.30); inverting the
censoring order fails
test_censored_control_only_run_still_measured_nothing.Compatibility
JSON output stays
"schema": 1, with two added fields. No CLI flags change.The
docs/package is documentation only — nothing in the harness imports it.Dependencies
None — branches off
main. First of six stages described inspec/DSPX-4372-t1.md(added here), which together replace #621.Summary by CodeRabbit
Bug Fixes
Documentation