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Claude
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Target selection (SPEC §6): comrak 0.53.0 (45c1995, BSD-2-Clause) and tokei 14.0.0 (fa44e51, MIT/Apache-2.0); both CPU-bound with pinned corpora (progit book 11MB; 8x replicated pinned trees, 221MB) and committed MANIFEST.sha256 + golden-output pins + regen scripts. Calibration: A/A null verdicts on both real workloads; taskset -c 2 pinning tightens the A/A CI from [0.938, 1.008] to [0.993, 1.008], making the 2% accept threshold meaningful in this container. Profiles (callgrind; perf unavailable): comrak allocator symbols 26.7% of Ir; tokei perform_multi_line_analysis 31.7%. Attempts (ledger + results/phase0/): - comrak class-1 target-cpu=native: null [0.983, 1.011], rejected-bench - comrak class-2 mimalloc swap: +4.6% [1.033, 1.058], 848 upstream tests green, golden byte-identical, ASan-proper clean; LSan flags 484B in onig (reachability false-positive analysis in case study) -> needs-human-review per SPEC §8 - tokei class-1 fat LTO+cgu=1: +1.6% [1.003, 1.026], real but under the 2% bar, rejected-bench Also: ledger-cli for manual rows, targets/ excluded from trust-layer workspace, corpora/build artifacts gitignored, case study written. Phase 0 exit criteria (>=10% verified win) not yet met; next hypotheses logged in results/phase0/attempts.md. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2
85 lines
4.4 KiB
Markdown
85 lines
4.4 KiB
Markdown
# Phase 0 dry-run attempt log
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Hypotheses are recorded here *before* any patch is applied; final
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evidence and verdicts go to the SQLite ledger and are mirrored here.
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Environment for the whole session: remote 4-core container
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(Intel Xeon @ 2.10GHz, kernel 6.18.5), governor/turbo not controllable,
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benches pinned with `taskset -c 2`. A/A calibration on both target
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workloads passed with pinning (see results/calibration/).
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## Deviations from SPEC (Phase 0 manual dry run)
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- No nested no-network container available (no docker daemon): target
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code runs in this session's own isolated ephemeral container, which
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serves as the sandbox. Phase 1 must restore the dedicated container.
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- `perf` unavailable (container): profiling via valgrind/callgrind
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(deterministic instruction counts, Ir), not cycle sampling. Ir% is a
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proxy for cycles%; it under-weights cache/branch effects.
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- Corpus files >10 MB are pinned by committed MANIFEST.sha256 +
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regeneration scripts rather than committed raw (repo bloat).
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## Attempt 1 — comrak, class 1 (build configuration)
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- **Logged**: 2026-07-06, before patching.
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- **Hotspot**: whole-program; upstream already ships lto=true +
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codegen-units=1, so classic class-1 flags are exhausted upstream.
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- **Hypothesis**: `RUSTFLAGS=-C target-cpu=native` (baseline ISA: the
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bench machine's Xeon) enables wider SIMD paths in string scanning
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(jetscii, memchr paths visible in profile) and better scheduling;
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expect a small win, 2-6% median speedup. No FP semantics change
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(integer/string workload; not a -ffast-math-class flag), so
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auto-acceptable if gates pass. Deploy caveat: win only valid for
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fleets whose ISA baseline matches; recorded in workload statement.
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- **Patch**: none (env-level build config); candidate built to a
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separate CARGO_TARGET_DIR from the same pinned commit.
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## Attempt 2 — comrak, class 2 (allocator swap)
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- **Logged**: 2026-07-06, before patching, after Attempt 1's hypothesis.
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- **Hotspot**: allocator symbols sum to ~26.7% of Ir (_int_malloc 9.99%,
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_int_free 6.85%, malloc 3.92%, malloc_consolidate 3.48%, free 2.49%)
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— the class-2 precondition (≥5%) is exceeded 5x.
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- **Hypothesis**: glibc malloc is the allocator; comrak's AST/inline
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parsing churns small allocations. Swapping the CLI's global allocator
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to mimalloc cuts allocator instructions substantially; expect 8-20%
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median speedup on the progit workload.
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- **Patch plan**: 2-line change in comrak CLI main + Cargo.toml dep,
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inside targets/comrak/workspace only.
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## Attempt 3 — tokei, class 1 (build configuration)
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- **Logged**: 2026-07-06, before patching.
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- **Hotspot**: whole-program; upstream ships lto="thin", panic="abort",
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default codegen-units (16).
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- **Hypothesis**: lto=true (fat) + codegen-units=1 lets the analysis
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loop (perform_multi_line_analysis, 31.7% Ir) inline across cgu and
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crate boundaries (memchr/aho-corasick calls visible in profile);
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expect 2-8% median speedup. No semantics change; auto-acceptable if
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golden replay passes.
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- **Patch**: [profile.release] lto = true, codegen-units = 1 in
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targets/tokei/workspace/Cargo.toml only.
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## Outcomes (ledger is authoritative: results/ledger.sqlite)
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| run_id | class | speedup median | 95% CI | verdict |
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|---|---|---|---|---|
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| phase0-comrak-001 | 1 build-config | 0.9965 | [0.9826, 1.0110] | rejected-bench (null) |
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| phase0-comrak-002 | 2 allocator | **1.0459** | **[1.0333, 1.0577]** | needs-human-review |
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| phase0-tokei-001 | 1 build-config | 1.0161 | [1.0026, 1.0262] | rejected-bench (< 2% threshold) |
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- comrak-002 gates: 848 upstream tests green on patched tree; golden
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replay byte-identical; pristine ASan+LSan clean; patched ASan-proper
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clean; LSan flags 484 B in onig (analysis: LSan × custom-allocator
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reachability false positive — see case-study-comrak.md). SPEC §8
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routes any sanitizer flag to human review, so that is the verdict.
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- tokei-001 is a *real but small* effect — CI excludes 1.0 but its
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lower bound (+0.26%) is under the 2% bar. Correctly rejected; logged
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so nobody re-grinds it.
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- Phase 0 exit criteria (≥1 verified win ≥10%) **not yet met**: best
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verified candidate is +4.6% pending human review. Next cheapest
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hypotheses per profile: comrak class 3 (allocation churn — arena the
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inline parser's Vec growth, RawVec::finish_grow 2.3% + memcpy 3.1%);
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tokei class 3 (memset 8.5% suggests per-file buffer zeroing) and
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class 5 (perform_multi_line_analysis 31.7% single frame).
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