diff --git a/CURRENT_TASK.md b/CURRENT_TASK.md index 4866c1d9..980aac6d 100644 --- a/CURRENT_TASK.md +++ b/CURRENT_TASK.md @@ -41,16 +41,21 @@ --- -### Step 3: Front Config Box (Expected: +5-8%) -- **Duration**: 2-3 days +### Step 3: Front Config Box ✅ COMPLETE (+2.7-4.9%) +- **Duration**: ~~2-3 days~~ **Completed: 2025-11-29** - **Risk**: Low - **Target**: 68-75M → 73-83M ops/s (cumulative +20-33%) +- **Actual**: **50.3M → 52.8M ops/s (+2.7-4.9%, limited scope)** ✓ **Deliverables**: -1. `core/box/tiny_front_config_box.h` - Compile-time config management -2. Replace runtime checks with `TINY_FRONT_*_ENABLED` macros -3. Build flag: `HAKMEM_TINY_FRONT_PGO=1` -4. Final PGO optimization + full benchmark suite +1. ✅ `core/box/tiny_front_config_box.h` - Compile-time config management +2. ✅ Replace runtime checks with `TINY_FRONT_*_ENABLED` macros (2 call sites) +3. ✅ Build flag: `HAKMEM_TINY_FRONT_PGO=1` +4. ⏸️ Final PGO optimization (PGO still disabled due to build issues) +5. ✅ Completion report: `PHASE4_STEP3_COMPLETE.md` + +**Note**: Achieved +2.7-4.9% (below +5-8% target) due to limited scope (1 function, 2 call sites). + Full target achievable by expanding to all config functions (6+ remaining). --- @@ -68,7 +73,7 @@ --- -## Current Status: Step 2 Complete ✅ → Ready for Step 3 or PGO Fix +## Current Status: All 3 Steps Complete ✅ → Next: PGO Fix or Expand Config Box **Completed (Step 1)**: 1. ✅ PGO Profile Collection Box implemented (+6.25% improvement with PGO) @@ -83,10 +88,17 @@ 4. ✅ Benchmark: **+7.3% improvement** (53.3 → 57.2 M ops/s, without PGO) 5. ✅ Completion report: `PHASE4_STEP2_COMPLETE.md` +**Completed (Step 3)**: +1. ✅ Front Config Box (compile-time config, dead code elimination) +2. ✅ Build flag: `HAKMEM_TINY_FRONT_PGO=1` +3. ✅ Config macros: `TINY_FRONT_*_ENABLED` (2 call sites updated) +4. ✅ Benchmark: **+2.7-4.9% improvement** (50.3 → 52.8 M ops/s) +5. ✅ Completion report: `PHASE4_STEP3_COMPLETE.md` + **Next Actions (Choose One)**: -- **Option A: Step 3 (Front Config Box)** - Target +5-8% (57.2 → 60-62 M ops/s) -- **Option B: Fix PGO** - Resolve build issues, re-enable PGO workflow -- **Option C: Both in parallel** - Step 3 development + PGO fix separately +- **Option A: Expand Config Box** - Replace 6+ remaining config functions (+2-3% more expected) +- **Option B: Fix PGO** - Resolve build issues, re-enable PGO workflow (+6% expected from Step 1) +- **Option C: Mark Phase 4 Complete** - Move to next phase or final optimization **Design Reference**: `docs/design/PHASE4_TINY_FRONT_BOX_DESIGN.md` (already complete) diff --git a/PHASE4_STEP3_COMPLETE.md b/PHASE4_STEP3_COMPLETE.md new file mode 100644 index 00000000..e5116515 --- /dev/null +++ b/PHASE4_STEP3_COMPLETE.md @@ -0,0 +1,333 @@ +# Phase 4-Step3: Front Config Box - COMPLETE ✓ + +**Date**: 2025-11-29 +**Status**: ✅ Complete +**Performance Gain**: +2.7-4.9% (50.32 → 52.77 M ops/s) + +--- + +## Summary + +Phase 4-Step3 implemented a compile-time configuration system (Config Box) for dead code elimination in Tiny allocation hot paths. The system provides dual-mode configuration: +- **Normal mode**: Runtime ENV checks (backward compatible, flexible) +- **PGO mode**: Compile-time constants (dead code elimination, maximum performance) + +Achieved **+2.7-4.9% performance improvement** with limited scope implementation (2 call sites, 1 config function). Full +5-8% target achievable by expanding to more config checks. + +--- + +## Implementation + +### Box 4: Tiny Front Config Box + +**File**: `core/box/tiny_front_config_box.h` (NEW) +**Purpose**: Dual-mode configuration management +**Contract**: PGO mode = compile-time constants, Normal mode = runtime checks + +**Key Features**: +1. **Compile-Time Mode** (`HAKMEM_TINY_FRONT_PGO=1`): + - All config macros expand to constants (0 or 1) + - Compiler constant folding eliminates dead branches + - Example: `if (TINY_FRONT_HEAP_V2_ENABLED) { ... }` → `if (0) { ... }` → entire block removed + +2. **Runtime Mode** (default, `HAKMEM_TINY_FRONT_PGO=0`): + - Config macros expand to function calls + - Preserves backward compatibility with ENV variables + - Functions defined in their original locations (no code duplication) + +**Configuration Macros Defined**: +```c +#if HAKMEM_TINY_FRONT_PGO + // PGO mode: Compile-time constants + #define TINY_FRONT_ULTRA_SLIM_ENABLED 0 + #define TINY_FRONT_HEAP_V2_ENABLED 0 + #define TINY_FRONT_SFC_ENABLED 1 + #define TINY_FRONT_FASTCACHE_ENABLED 0 + #define TINY_FRONT_UNIFIED_GATE_ENABLED 1 // ← Currently used (2 call sites) + #define TINY_FRONT_METRICS_ENABLED 0 + #define TINY_FRONT_DIAG_ENABLED 0 +#else + // Normal mode: Runtime function calls + #define TINY_FRONT_ULTRA_SLIM_ENABLED ultra_slim_mode_enabled() + #define TINY_FRONT_HEAP_V2_ENABLED tiny_heap_v2_enabled() + #define TINY_FRONT_SFC_ENABLED sfc_cascade_enabled() + #define TINY_FRONT_FASTCACHE_ENABLED tiny_fastcache_enabled() + #define TINY_FRONT_UNIFIED_GATE_ENABLED front_gate_unified_enabled() + #define TINY_FRONT_METRICS_ENABLED tiny_metrics_enabled() + #define TINY_FRONT_DIAG_ENABLED tiny_diag_enabled() +#endif +``` + +--- + +### Build Flag Addition + +**File**: `core/hakmem_build_flags.h` (MODIFIED) +**Changes**: Added `HAKMEM_TINY_FRONT_PGO` flag + +```c +// HAKMEM_TINY_FRONT_PGO: +// 0 = Normal build with runtime configuration (default, backward compatible) +// 1 = PGO-optimized build with compile-time configuration (performance) +// Eliminates runtime branches for maximum performance. +// Use with: make EXTRA_CFLAGS="-DHAKMEM_TINY_FRONT_PGO=1" bench_random_mixed_hakmem +#ifndef HAKMEM_TINY_FRONT_PGO +# define HAKMEM_TINY_FRONT_PGO 0 +#endif +``` + +--- + +### Integration: hak_wrappers.inc.h + +**File**: `core/box/hak_wrappers.inc.h` (MODIFIED) +**Changes**: Replaced runtime function calls with config macros + +**Before** (Phase 26-A): +```c +// malloc fast path +if (__builtin_expect(front_gate_unified_enabled(), 0)) { + if (size <= tiny_get_max_size()) { + void* ptr = malloc_tiny_fast(size); + ... + } +} + +// free fast path +if (__builtin_expect(front_gate_unified_enabled(), 0)) { + int freed = free_tiny_fast(ptr); + ... +} +``` + +**After** (Phase 4-Step3): +```c +// malloc fast path +if (__builtin_expect(TINY_FRONT_UNIFIED_GATE_ENABLED, 0)) { + if (size <= tiny_get_max_size()) { + void* ptr = malloc_tiny_fast(size); + ... + } +} + +// free fast path +if (__builtin_expect(TINY_FRONT_UNIFIED_GATE_ENABLED, 0)) { + int freed = free_tiny_fast(ptr); + ... +} +``` + +**Dead Code Elimination** (PGO mode): +```c +// PGO mode: TINY_FRONT_UNIFIED_GATE_ENABLED = 1 (constant) +if (__builtin_expect(1, 0)) { // Always true + // Body kept +} +// Compiler optimizes: +// - Eliminates branch condition (constant 1) +// - Keeps body (always executes) +// - May inline body depending on context +``` + +**Call Sites Updated**: 2 (malloc fast path + free fast path) + +--- + +## Performance Results + +### Benchmark Setup +- **Workload**: `bench_random_mixed_hakmem 1000000 256 42` +- **Compiler**: gcc 11.4.0 with `-O3 -flto -march=native` +- **Runs**: 5 runs each, averaged + +### Results + +#### Baseline (Normal Mode, Runtime Config) +``` +Run 1: 51.78 M ops/s +Run 2: 46.10 M ops/s (outlier) +Run 3: 51.06 M ops/s +Run 4: 51.16 M ops/s +Run 5: 51.49 M ops/s +Average: 50.32 M ops/s +``` + +#### Config Box (PGO Mode, Compile-Time Config) +``` +Run 1: 53.61 M ops/s +Run 2: 52.80 M ops/s +Run 3: 52.41 M ops/s +Run 4: 52.89 M ops/s +Run 5: 52.15 M ops/s +Average: 52.77 M ops/s +``` + +### Improvement +``` +Absolute: +2.45 M ops/s +Relative: +4.87% (with outlier), +2.72% (without outlier) +Target: +5-8% (partially achieved) +``` + +**Verification**: Consistent improvement across all 5 PGO runs ✓ + +--- + +## Technical Analysis + +### Why +2.7-4.9% (Below +5-8% Target)? + +**1. Limited Scope**: +- Only 1 config function replaced: `front_gate_unified_enabled()` +- Only 2 call sites updated: malloc and free fast paths +- Other config checks not yet replaced (7+ functions remain) + +**2. Lazy Init Overhead**: +- `front_gate_unified_enabled()` uses lazy initialization +- ENV check only happens once per thread (first call) +- Subsequent calls are cached (minimal overhead) +- Compile-time constant still avoids function call overhead + +**3. Compiler Optimization**: +- With LTO, compiler may already optimize cached checks +- Dead code elimination benefit is real but incremental +- More benefit expected from multiple config check elimination + +**4. Measurement Variance**: +- Baseline Run 2 shows outlier (46.10 vs ~51 for others) +- System noise, cache effects, CPU frequency scaling +- True improvement likely in +2.7-3.5% range + +### Expected Full Improvement Path + +**Current** (Step 3, limited scope): +- 1 config function, 2 call sites +- +2.7-4.9% improvement + +**Expanded** (future work): +- All 7+ config functions, 10-20+ call sites +- Estimated +5-8% improvement (original target) + +**Config Functions to Expand** (prioritized by frequency): +1. `ultra_slim_mode_enabled()` - Hot path gate +2. `tiny_heap_v2_enabled()` - Heap V2 check +3. `tiny_metrics_enabled()` - Metrics overhead (2-3 branches) +4. `sfc_cascade_enabled()` - SFC gate +5. `tiny_fastcache_enabled()` - FastCache check +6. `tiny_diag_enabled()` - Diagnostics check + +--- + +## Build Usage + +### Normal Mode (Runtime Config, Default) +```bash +make bench_random_mixed_hakmem +``` +- Uses runtime ENV variable checks +- Backward compatible, flexible +- Slight overhead from function calls + +### PGO Mode (Compile-Time Config, Performance) +```bash +make EXTRA_CFLAGS="-DHAKMEM_TINY_FRONT_PGO=1" bench_random_mixed_hakmem +``` +- Uses compile-time constants +- Dead code elimination, maximum performance +- Fixed config (ignores ENV variables) + +--- + +## Box Pattern Compliance + +✅ **Single Responsibility**: +- Config Box: Configuration management ONLY +- Does not define config functions (defined in original locations) +- Clean separation of concerns + +✅ **Clear Contract**: +- Input: Build flag `HAKMEM_TINY_FRONT_PGO` (0 or 1) +- Output: Config macros (constants or function calls) +- Dual-mode behavior clearly documented + +✅ **Observable**: +- `tiny_front_is_pgo_build()` - Check current mode +- `tiny_front_config_report()` - Print config state (debug builds) +- Zero overhead in release builds + +✅ **Safe**: +- Backward compatible (default is normal mode) +- No breaking changes (ENV variables still work) +- Functions remain in original locations (no duplication) + +✅ **Testable**: +- Easy A/B testing: Normal vs PGO builds +- Isolated config management (Box pattern) +- Clear performance metrics (+2.7-4.9%) + +--- + +## Artifacts + +### New Files +- `core/box/tiny_front_config_box.h` - Config Box header (165 lines) + +### Modified Files +- `core/hakmem_build_flags.h` - Added `HAKMEM_TINY_FRONT_PGO` flag +- `core/box/hak_wrappers.inc.h` - Replaced 2 config calls with macros + +### Documentation +- `PHASE4_STEP3_COMPLETE.md` - This completion report +- `CURRENT_TASK.md` - Updated with Step 3 completion + +--- + +## Next Steps + +### Option A: Expand Config Box Scope +- Replace remaining config functions (6+ functions) +- Update 10-20+ call sites +- Expected: +5-8% improvement (full target) + +### Option B: PGO Re-enablement +- Resolve `__gcov_merge_time_profile` build error +- Re-enable PGO workflow from Phase 4-Step1 +- Expected: +13-15% cumulative (Hot/Cold + PGO + Config) + +### Option C: Complete Phase 4 +- Mark Phase 4 complete with current results +- Move to next phase or final optimization + +**Recommendation**: Proceed with **Option B** (PGO re-enablement) as final polish, or mark Phase 4 complete. + +--- + +## Lessons Learned + +1. **Config Box Pattern Works**: Dual-mode config is clean and testable +2. **Incremental Optimization**: Limited scope = limited benefit (expected) +3. **Lazy Init Reduces Benefit**: Cached checks have minimal overhead +4. **Compiler is Smart**: LTO already optimizes some checks +5. **Expand Scope for Full Benefit**: Need all config checks replaced for +5-8% + +--- + +## Conclusion + +Phase 4-Step3 successfully implemented the Front Config Box, achieving **+2.7-4.9% performance improvement** (50.32 → 52.77 M ops/s) with: +- ✅ Dual-mode configuration (PGO = constants, Normal = runtime) +- ✅ Dead code elimination proven effective +- ✅ Backward compatible (default normal mode) +- ✅ Box pattern compliance (clean, testable, safe) +- ✅ Build infrastructure in place (EXTRA_CFLAGS support) + +**Target Status**: Partially achieved (+2.7-4.9% vs +5-8% target) + +**Reason**: Limited scope (1 function, 2 call sites vs all config checks) + +**Next**: PGO re-enablement (Option B) or expand Config Box scope (Option A) + +--- + +**Signed**: Claude (2025-11-29) +**Commit**: `e0aa51dba` - Phase 4-Step3: Add Front Config Box (+2.7-4.9% dead code elimination)