Phase 10: TLS/SFC aggressive cache tuning (syscall reduction failed)

Goal: Reduce backend transitions by increasing frontend hit rate
Result: +2% best case, syscalls unchanged (root cause: SuperSlab churn)

Implementation:

1. Cache capacity expansion (2-8x per-class)
   - Hot classes (C0-C3): 4x increase (512 slots)
   - Medium classes (C4-C6): 2-3x increase
   - Class 7 (1KB): 2x increase (128 slots)
   - Fast cache: 2x default capacity

2. Refill batch size increase (4-8x)
   - Global default: 16 → 64 (4x)
   - Hot classes: 128 (8x) via HAKMEM_TINY_REFILL_COUNT_HOT
   - Mid classes: 96 (6x) via HAKMEM_TINY_REFILL_COUNT_MID
   - Class 7: 64 → 128 (2x)
   - SFC refill: 64 → 128 (2x)

3. Adaptive sizing aggressive parameters
   - Grow threshold: 80% → 70% (expand earlier)
   - Shrink threshold: 20% → 10% (shrink less)
   - Growth rate: 2x → 1.5x (smoother growth)
   - Max capacity: 2048 → 4096 (2x ceiling)
   - Adapt frequency: Every 10 → 5 refills (more responsive)

Performance Results (100K iterations):

Before (Phase 9):
- Performance: 9.71M ops/s
- Syscalls: 1,729 (mmap:877, munmap:852)

After (Phase 10):
- Default settings: 8.77M ops/s (-9.7%) ⚠️
- Optimal ENV: 9.89M ops/s (+2%) ✅
- Syscalls: 1,729 (unchanged) ❌

Optimal ENV configuration:
export HAKMEM_TINY_REFILL_COUNT_HOT=256
export HAKMEM_TINY_REFILL_COUNT_MID=192

Root Cause Analysis:

Bottleneck is NOT TLS/SFC hit rate, but SuperSlab allocation churn:
- 877 SuperSlabs allocated (877MB via mmap)
- Phase 9 LRU cache not utilized (no frees during benchmark)
- All SuperSlabs retained until program exit
- System malloc: 9 syscalls vs HAKMEM: 1,729 syscalls (192x gap)

Conclusion:

TLS/SFC tuning cannot solve SuperSlab allocation policy problem.
Next step: Phase 11 SuperSlab Prewarm strategy to eliminate
mmap/munmap during benchmark execution.

ChatGPT review: Strategy validated, Option A (Prewarm) recommended.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

core/hakmem_tiny_config.h

@@ -146,10 +146,11 @@ int tiny_cap_max_for_class(int class_idx);
 extern int g_sfc_enabled;
 
 // SFC Default Configuration (can be overridden via ENV)
-// ENV: HAKMEM_SFC_CAPACITY (default: 128, range: 16-256)
-// ENV: HAKMEM_SFC_REFILL_COUNT (default: 64, range: 8-256)
-#define SFC_DEFAULT_CAPACITY 128
-#define SFC_DEFAULT_REFILL_COUNT 64
+// Phase 10: Aggressive SFC defaults to maximize front cache hit rate
+// ENV: HAKMEM_SFC_CAPACITY (default: 256, range: 16-512)
+// ENV: HAKMEM_SFC_REFILL_COUNT (default: 128, range: 8-256)
+#define SFC_DEFAULT_CAPACITY 256
+#define SFC_DEFAULT_REFILL_COUNT 128
 
 // SFC Per-Class Overrides (optional)
 // ENV: HAKMEM_SFC_CAPACITY_CLASS{0..7} (per-class capacity)