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94f9ea5104
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Implement Phase 1: TLS SuperSlab Hint Box for Headerless performance
Design: Cache recently-used SuperSlab references in TLS to accelerate
ptr→SuperSlab resolution in Headerless mode free() path.
## Implementation
### New Box: core/box/tls_ss_hint_box.h
- Header-only Box (4-slot FIFO cache per thread)
- Functions: tls_ss_hint_init(), tls_ss_hint_update(), tls_ss_hint_lookup(), tls_ss_hint_clear()
- Memory overhead: 112 bytes per thread (negligible)
- Statistics API for debug builds (hit/miss counters)
### Integration Points
1. **Free path** (core/hakmem_tiny_free.inc):
- Lines 477-481: Fast path hint lookup before hak_super_lookup()
- Lines 550-555: Second lookup location (fallback path)
- Expected savings: 10-50 cycles → 2-5 cycles on cache hit
2. **Allocation path** (core/tiny_superslab_alloc.inc.h):
- Lines 115-122: Linear allocation return path
- Lines 179-186: Freelist allocation return path
- Cache update on successful allocation
3. **TLS variable** (core/hakmem_tiny_tls_state_box.inc):
- `__thread TlsSsHintCache g_tls_ss_hint = {0};`
### Build System
- **Build flag** (core/hakmem_build_flags.h):
- HAKMEM_TINY_SS_TLS_HINT (default: 0, disabled)
- Validation: requires HAKMEM_TINY_HEADERLESS=1
- **Makefile**:
- Removed old ss_tls_hint_box.o (conflicting implementation)
- Header-only design eliminates compiled object files
### Testing
- **Unit tests** (tests/test_tls_ss_hint.c):
- 6 test functions covering init, lookup, FIFO rotation, duplicates, clear, stats
- All tests PASSING
- **Build validation**:
- ✅ Compiles with hint disabled (default)
- ✅ Compiles with hint enabled (HAKMEM_TINY_SS_TLS_HINT=1)
### Documentation
- **Benchmark report** (docs/PHASE1_TLS_HINT_BENCHMARK.md):
- Implementation summary
- Build validation results
- Benchmark methodology (to be executed)
- Performance analysis framework
## Expected Performance
- **Hit rate**: 85-95% (single-threaded), 70-85% (multi-threaded)
- **Cycle savings**: 80-95% on cache hit (10-50 cycles → 2-5 cycles)
- **Target improvement**: 15-20% throughput increase vs Headerless baseline
- **Memory overhead**: 112 bytes per thread
## Box Theory
**Mission**: Cache hot SuperSlabs to avoid global registry lookup
**Boundary**: ptr → SuperSlab* or NULL (miss)
**Invariant**: hint.base ≤ ptr < hint.end → hit is valid
**Fallback**: Always safe to miss (triggers hak_super_lookup)
**Thread Safety**: TLS storage, no synchronization required
**Risk**: Low (read-only cache, fail-safe fallback, magic validation)
## Next Steps
1. Run full benchmark suite (sh8bench, cfrac, larson)
2. Measure actual hit rate with stats enabled
3. If performance target met (15-20% improvement), enable by default
4. Consider increasing cache slots if hit rate < 80%
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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2025-12-03 18:06:24 +09:00 |
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