b1912d6587
## Summary Phase 18 v1 attempted layout optimization using section splitting + GC: - `-ffunction-sections -fdata-sections -Wl,--gc-sections` Result: **Catastrophic I-cache regression** - Throughput: -0.87% (48.94M → 48.52M ops/s) - I-cache misses: +91.06% (131K → 250K) - Variance: +80% (σ=0.45M → σ=0.81M) Root cause: Section-based splitting without explicit hot symbol ordering fragments code locality, destroying natural compiler/LTO layout. ## Build Knob Safety Makefile updated to separate concerns: - `HOT_TEXT_ISOLATION=1` → attributes only (safe, but no perf gain) - `HOT_TEXT_GC_SECTIONS=1` → section splitting (currently NO-GO) Both kept as research boxes (default OFF). ## Verdict Freeze Phase 18 v1: - Do NOT use section-based linking without strong ordering strategy - Keep hot/cold attributes as placeholder (currently unused) - Proceed to Phase 18 v2: BENCH_MINIMAL compile-out Expected impact v2: +10-20% via instruction count reduction - GO threshold: +5% minimum, +8% preferred - Only continue if instructions clearly drop ## Files New: - docs/analysis/PHASE18_HOT_TEXT_ISOLATION_1_AB_TEST_RESULTS.md Modified: - Makefile (build knob safety isolation) - CURRENT_TASK.md (Phase 18 v1 verdict) - docs/analysis/PHASE18_HOT_TEXT_ISOLATION_1_NEXT_INSTRUCTIONS.md ## Lessons 1. Layout optimization is extremely fragile without ordering guarantees 2. I-cache is first-order performance factor (IPC=2.30 is memory-bound) 3. Compiler defaults may be better than manual section splitting 4. Next frontier: instruction count reduction (stats/ENV removal) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Docs Overview
このフォルダは hakmem の設計・計測・運用メモを体系化して管理する場所です。
- INDEX.md: 目次（各ドキュメントへのリンク）
- benchmarks/: ベンチマーク手順とスイープ結果の保存先
- specs/: 現在の仕様（SACS‑3/HW/ENV）を集約
- roadmap/: これからの実装計画・優先度・タスク
運用ルール（提案）
- 1つの変更/計測のまとまりにつき1ファイル（or 1フォルダ）
- 再現コマンド・環境変数・ハード構成は必ず記載
- 大きな連続出力はファイルへ保存し、本文からは抜粋/要約を記載