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perf(bench): add a fixed-iteration Ir/op gate for the hot paths (LAB-7802) - #106
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…7802) Wall clock cannot gate a 1% CPU regression on a shared machine, and the Criterion suite picks its iteration count from wall time, so its total under valgrind cannot be divided by a known count. benches/perf_ir.rs runs each case in its own process under cachegrind, once with 1,000 calls and once with none, after the same setup and one warm-up call: Ir/op = (Ir[1000] - Ir[0]) / 1000. Cases cover ByteStorage store/retrieve, the envelope pre-scan, AES-256-GCM encrypt/decrypt, the keyring decrypt (HKDF per call), the tenant keyring decrypt, and HKDF, at 64 B, 1 KiB and 64 KiB. `make perf-ir` compares against benches/perf_ir_baselines.json (fail at +1%, warn from +0.2%); `make perf-ir-update` ratchets budgets down, never up without --allow-increase. Two runs of one build agree exactly; between builds, heap alignment moves encrypt/1024 by up to 0.19% and every other case by at most 0.02%. The target is `bench = false`, so a plain `cargo bench` does not need valgrind, and `clippy --all-targets` still compiles it. hot_path's realistic payload generator moves to benches/common so both targets measure the same bytes. No new dependency.
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Summary by CodeRabbit
WalkthroughThe pull request adds a Cachegrind instruction-count benchmark with platform-specific budgets and commands to run or update them. It also adds shared deterministic benchmark helpers and updates the README with benchmark details. ChangesPerformance benchmarks
Priority: ⬇️ Low Estimated code review effort: 4 (Complex) | ~45 minutes Change: Other Sequence Diagram(s)sequenceDiagram
participant Gate as perf_ir gate
participant Cachegrind
participant Runner as Measured-process runner
Gate->>Cachegrind: Measure case with N_OPS and zero operations
Cachegrind->>Runner: Run case with operation count
Runner-->>Cachegrind: Return after warm-up and requested operations
Cachegrind-->>Gate: Return instruction counts
Gate->>Gate: Subtract setup count
Merge Risk: 🔵 Low · up to Partial budget updates can hide a toolchain mismatch for unmeasured cases. The local gate remains usable, but its metadata should be corrected before relying on those comparisons. Security Architecture ReviewSecurity architecture risk: ⚪ Minimal · up to The gate uses deterministic benchmark inputs and explicitly requested budget updates. No material security risk was identified. Update failures and concurrent invocations can affect local benchmark budgets, but the inspected flow does not change production authorization, tenant state, or deployment configuration. 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 52.94% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 3 files. (4 skipped: 4 unsupported.) ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Review comments at @benches/perf_ir.rs:
- Around line 324-331: In the update flow around ratchet, only update
platform.rustc and platform.valgrind when the measurement covers every case.
Capture the total case count before cases are filtered, then compare it with
measured.len(); leave the existing toolchain versions unchanged for partial
updates.
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Cargo.tomlMakefileREADME.mdbenches/common/mod.rsbenches/hot_path.rsbenches/perf_ir.rsbenches/perf_ir_baselines.json
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…802) A budget set gates only the instrument that recorded it. Two ways let `--update` mix instruments: - Budgets were keyed by architecture and OS only. A build with `-C target-cpu=x86-64-v3` measures hkdf at 23,913 Ir/op against the default build's 29,047, so ratcheting from it lowered the shared set and then failed every default build of unchanged code. The key now appends any compiled-in CPU features, so such a build records its own set. - `--update` stamped the current rustc and valgrind on every run, including a `--case` subset and a run whose regression stayed over budget, so budgets it never measured carried the new versions and the mismatch note went silent. On a toolchain other than the recorded one, `--update` now refuses unless it re-records every case with `--allow-increase`.
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Adds
make perf-ir: a per-op instruction count (Ir/op) for each hot path, a committed budget per case, and a gate that fails at +1% and ratchets budgets down. Closes LAB-7802.Why
Wall clock on a shared machine moves by far more than 1% between identical runs, so it cannot gate a small CPU regression. The Criterion suite (
hot_path) also picks its iteration count from wall time, so its total under valgrind cannot be divided by a known count. A fixed iteration count under cachegrind is exact.What
benches/perf_ir.rsruns each case in its own process undervalgrind --tool=cachegrind --cache-sim=no. It runs once with 1,000 calls and once with none, after the same setup and one warm-up call, soIr/op = (Ir[1000] - Ir[0]) / 1000and process start, setup and exit cancel. The measured process gets an empty environment.store,retrieve,prescan,encrypt,decrypt,keyring_decryptandtenant_keyring_decrypt, each at 64 B, 1 KiB and 64 KiB, plushkdf, which takes no payload.benches/perf_ir_baselines.json, keyed by architecture and OS, with the rustc and valgrind versions they were recorded with. A case fails at +1% and warns from +0.2%.make perf-ir-updateonly lowers budgets; raising one takesARGS=--allow-increase.bench = falsekeeps the target out of a plaincargo bench, so nobody needs valgrind for Criterion.clippy --all-targetsstill compiles it, so it cannot rot unnoticed.benches/common, so both targets measure the same bytes.Evidence
decrypt/65536encrypt/1024−0.19%, every other case ≤ 0.02%encrypt/1024is bimodal by alignment (6,420 or 6,432 Ir/op); every other case spreads ≤ 0.022%ByteStorage::storestore/64+0.41% WARN,store/1024+2.38% FAIL,store/65536+3.58% FAIL, exit 1; the other 19 cases +0.00%--updatekeeps a regressed budget (exit 1) and--allow-increaseraises it; a missing budget fails; an unknown case, a missing valgrind or a bad flag exits 2cargo fmt --check,cargo clippy(all features;encryptionwith all targets; all features with all targets) andcargo test --all-featurespass. The hot_path msgpack corpus runs in Criterion--testmode.Not in this PR
CI wiring. The gate is local, like the rest of the Makefile's perf targets.