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19056282b6
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Phase 3 D2: Wrapper Env Cache - [DECISION: NO-GO]
Target: Reduce wrapper_env_cfg() overhead in malloc/free hot path
- Strategy: Cache wrapper env configuration pointer in TLS
- Approach: Fast pointer cache (TLS caches const wrapper_env_cfg_t*)
Implementation:
- core/box/wrapper_env_cache_env_box.h: ENV gate (HAKMEM_WRAP_ENV_CACHE)
- core/box/wrapper_env_cache_box.h: TLS cache layer (wrapper_env_cfg_fast)
- core/box/hak_wrappers.inc.h: Integration into malloc/free hot paths
- ENV gate: HAKMEM_WRAP_ENV_CACHE=0/1 (default OFF)
A/B Test Results (Mixed, 10-run, 20M iters):
- Baseline (D2=0): 46.52M ops/s (avg), 46.47M ops/s (median)
- Optimized (D2=1): 45.85M ops/s (avg), 45.98M ops/s (median)
- Improvement: avg -1.44%, median -1.05% (DECISION: NO-GO)
Analysis:
- Regression cause: TLS cache adds overhead (branch + TLS access)
- wrapper_env_cfg() is already minimal (pointer return after simple check)
- Adding TLS caching layer makes it worse, not better
- Branch prediction penalty outweighs any potential savings
Cumulative Phase 2-3:
- B3: +2.89%, B4: +1.47%, C3: +2.20%
- D1: +1.06% (opt-in), D2: -1.44% (NO-GO)
- Total: ~7.2% (excluding D2)
Decision: FREEZE as research box (default OFF, regression confirmed)
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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2025-12-13 22:03:27 +09:00 |
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d0b931b197
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Phase 3 C1: TLS Prefetch Implementation - NEUTRAL Result (Research Box)
Step 1 & 2 Complete:
- Implemented: core/front/malloc_tiny_fast.h prefetch (lines 264-267, 331-334)
- LEGACY path prefetch of g_unified_cache[class_idx] to L1
- ENV gate: HAKMEM_TINY_PREFETCH=0/1 (default OFF)
- Conditional: only when prefetch enabled + route_kind == LEGACY
- A/B test (Mixed 10-run): PREFETCH=0 (39.33M) → =1 (39.20M) = -0.34% avg
- Median: +1.28% (within ±1.0% neutral range)
- Result: 🔬 NEUTRAL (research box, default OFF)
Decision: FREEZE as research box
- Average -0.34% suggests prefetch overhead > benefit
- Prefetch timing too late (after route_kind selection)
- TLS cache access is already fast (head/tail indices)
- Actual memory wait happens at slots[] array access (after prefetch)
Technical Learning:
- Prefetch effectiveness depends on L1 miss rate at access time
- Inserting prefetch after route selection may be too late
- Future approach: move prefetch earlier or use different target
Next: Phase 3 C2 (Metadata Cache Optimization, expected +5-10%)
🤖 Generated with Claude Code
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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2025-12-13 19:01:57 +09:00 |
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