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hakmem/docs/analysis
Moe Charm (CI) 9ed8b9c79a Phase 27-28: Unified Cache stats validation + BG Spill audit
Phase 27: Unified Cache Stats A/B Test - GO (+0.74%)
- Target: g_unified_cache_* atomics (6 total) in WARM refill path
- Already implemented in Phase 23 (HAKMEM_TINY_UNIFIED_CACHE_MEASURE_COMPILED)
- A/B validation: Baseline 52.94M vs Compiled-in 52.55M ops/s
- Result: +0.74% mean, +1.01% median (both exceed +0.5% GO threshold)
- Impact: WARM path atomics have similar impact to HOT path
- Insight: Refill frequency is substantial, ENV check overhead matters

Phase 28: BG Spill Queue Atomic Audit - NO-OP
- Target: g_bg_spill_* atomics (8 total) in background spill subsystem
- Classification: 8/8 CORRECTNESS (100% untouchable)
- Key finding: g_bg_spill_len is flow control, NOT telemetry
  - Used in queue depth limiting: if (qlen < target) {...}
  - Operational counter (affects behavior), not observational
- Lesson: Counter name ≠ purpose, must trace all usages
- Result: NO-OP (no code changes, audit documentation only)

Cumulative Progress (Phase 24-28):
- Phase 24 (class stats): +0.93% GO
- Phase 25 (free stats): +1.07% GO
- Phase 26 (diagnostics): -0.33% NEUTRAL
- Phase 27 (unified cache): +0.74% GO
- Phase 28 (bg spill): NO-OP (audit only)
- Total: 17 atomics removed, +2.74% improvement

Documentation:
- PHASE27_UNIFIED_CACHE_STATS_RESULTS.md: Complete A/B test report
- PHASE28_BG_SPILL_ATOMIC_AUDIT.md: Detailed CORRECTNESS classification
- PHASE28_BG_SPILL_ATOMIC_PRUNE_RESULTS.md: NO-OP verdict and lessons
- ATOMIC_PRUNE_CUMULATIVE_SUMMARY.md: Updated with Phase 27-28
- CURRENT_TASK.md: Phase 29 candidate identified (Pool Hotbox v2)

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
2025-12-16 06:12:17 +09:00
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