hakmem/CURRENT_TASK.md

# Current Task: Choose Next Phase

**Date**: 2025-11-29
**Status**: Phase 5 ✅ COMPLETE → Next phase selection
**Achievement**: +28.9x improvement for Mid MT allocations (1KB-8KB)

---

## Phase 5 Complete! ✅

**Result**: Mid/Large Allocation Optimization **COMPLETE**
**Performance**: 1.49M → 41.0M ops/s (+28.9x for Mid MT, 1.53x faster than system malloc)
**Duration**: 1 day (focused execution)

**Completed Steps**:
- ✅ Step 1: Mid MT Verification (range bug identified)
- ✅ Step 2: Mid Free Route Box (+28.9x improvement)
- ✅ Step 3: Mid/Large Config Box (future workload infrastructure)
- ⏸️ Step 4: Mid Registry Pre-alloc (deferred, MT workload needed)
- ✅ Step 5: Documentation (PHASE5_COMPLETION_REPORT.md)

**See**: `PHASE5_COMPLETION_REPORT.md` for full details

---

## Next Phase Options

### Option A: Investigate bench_random_mixed Regression 🔍
**Goal**: Understand -8.6% regression in Tiny workload (57.2M → 52.3M ops/s)
**Hypothesis**: Binary size increase, cache effects, or compiler optimization changes
**Expected**: Identify cause, potential fix to recover lost performance
**Duration**: 2-3 days
**Risk**: Medium (may not be fixable, could be noise)

**Pros**:
- Recover potential 5-8% lost performance
- Understand impact of code size on cache behavior
- Clean up any unintended regressions

**Cons**:
- May be system noise (not real regression)
- Workload is Tiny-only (unaffected by Phase 5 changes)
- Could be time spent on noise instead of real gains

---

### Option B: PGO Re-enablement 🚀
**Goal**: Re-enable PGO workflow from Phase 4-Step1
**Expected**: +6-13% cumulative improvement (Hot/Cold + PGO + Config)
**Duration**: 2-3 days (resolve build issues)
**Risk**: Low (proven pattern, just needs cleanup)

**Pros**:
- Known benefit (+6.25% from Phase 4-Step1)
- Proven workflow (just needs `__gcov_merge_time_profile` fix)
- Cumulative with Hot/Cold Box (+7.3%)

**Cons**:
- Build infrastructure work (not algorithmic improvement)
- May have compatibility issues with newer gcc

**Phase 4 PGO Results** (reference):
- Before: 57.0 M ops/s
- After PGO: 60.6 M ops/s (+6.25%)

---

### Option C: Expand Tiny Front Config Box 📦
**Goal**: Complete Phase 4-Step3 by expanding Config Box to all 7 config functions
**Expected**: +5-8% improvement (original target, currently +2.7-4.9%)
**Duration**: 3-4 days
**Risk**: Low (proven pattern from Phase 4-Step3)

**Pros**:
- Known pattern (Phase 4-Step3 proved concept)
- Clear path: Replace 6 remaining config functions
- Predictable benefit based on Phase 4 results

**Cons**:
- Incremental work (not new innovation)
- Requires updating 10-20+ call sites

**Phase 4-Step3 Results** (reference):
- Limited scope (1 function): +2.7-4.9%
- Full scope (7 functions): +5-8% expected

---

### Option D: Production Readiness & Benchmarking 📊
**Goal**: Comprehensive benchmark suite, production deployment planning
**Expected**: Full performance comparison, stability testing, deployment guide
**Duration**: 3-5 days
**Risk**: Low (documentation + testing)

**Pros**:
- Comprehensive performance report (all allocators)
- Production readiness validation
- Deployment guide for users
- Clear performance story for stakeholders

**Cons**:
- No new performance gains
- Mostly documentation work

**Deliverables**:
- Full benchmark report (Tiny, Mid, Large, MT)
- Production deployment guide
- Performance comparison vs mimalloc/jemalloc/tcmalloc
- Stability/leak testing results

---

### Option E: Multi-threaded Optimization (MT Workloads) 🔀
**Goal**: Optimize for multi-threaded workloads (complete Phase 5-Step4)
**Expected**: Improved MT scalability, reduced lock contention
**Duration**: 4-6 days (need to create MT benchmarks first)
**Risk**: High (no MT benchmark exists yet)

**Pros**:
- Unlock Phase 5-Step4 (Mid registry pre-allocation)
- Real-world workloads are often MT
- Could show significant MT scalability gains

**Cons**:
- Need to create MT benchmarks first (2-3 days)
- Complexity: Lock-free data structures, atomic operations
- Hard to measure correctly (CPU pinning, NUMA, etc.)

**Required Work**:
1. Create MT benchmark (4+ threads, mixed sizes)
2. Profile MT contention points
3. Implement registry pre-allocation
4. Add lock-free structures where needed
5. Validate MT correctness (TSAN, stress testing)

---

## Recommendation

### Top Pick: **Option B (PGO Re-enablement)** 🚀

**Reasoning**:
1. **Known benefit**: +6.25% proven in Phase 4-Step1
2. **Low risk**: Just need to fix build issue (resolve `__gcov_merge_time_profile` error)
3. **Cumulative**: Stacks with Hot/Cold Box (+7.3%) and Config Box
4. **Quick win**: 2-3 days vs 4-6 days for MT work
5. **Production value**: PGO is standard practice for high-performance software

**Expected Cumulative Result** (if PGO works):
```
Phase 3 baseline:  56.8 M ops/s
Phase 4 Hot/Cold:  57.2 M ops/s (+0.7%, without PGO)
Phase 4 PGO:       60.6 M ops/s (+6.8% cumulative)
Phase 4 Config:    ~62-64 M ops/s (+9-13% cumulative)
```

**Fallback**: If PGO fix takes >3 days, switch to Option C (Expand Config Box)

---

### Second Choice: **Option C (Expand Tiny Front Config Box)** 📦

**Reasoning**:
1. **Proven pattern**: Phase 4-Step3 showed +2.7-4.9% with limited scope
2. **Clear path**: Known work (replace 6 config functions, 10-20 call sites)
3. **Predictable**: Expected +5-8% total (vs current +2.7-4.9%)
4. **Completion**: Finishes Phase 4-Step3 properly

**Expected Result**:
```
Phase 4-Step3 (limited): 52.8 M ops/s (+2.7-4.9%)
Phase 4-Step3 (full):    ~55-58 M ops/s (+5-8% expected)
```

---

### Third Choice: **Option D (Production Readiness)** 📊

**Reasoning**:
1. **Stakeholder value**: Clear performance story, deployment guide
2. **Comprehensive**: Full benchmark suite (not just random_mixed)
3. **Real-world**: Test stability, leaks, multi-threaded correctness
4. **Pause point**: Good time to consolidate before more optimization

**Deliverables**:
- Benchmark report comparing all allocators
- Performance vs competitors (mimalloc, jemalloc, etc.)
- Production deployment guide
- Stability testing results

---

## Current Performance Summary

### bench_random_mixed (16B-1KB, Tiny workload)
```
Phase 3 (mincore removal):     56.8 M ops/s
Phase 4 (Hot/Cold Box):         57.2 M ops/s (+0.7%)
Phase 5 (current):              52.3 M ops/s (-8.6% regression)
```
**Note**: Regression unrelated to Phase 5 (Tiny-only workload, doesn't touch Mid MT)

### bench_mid_mt_gap (1KB-8KB, Mid MT workload)
```
Before Phase 5 (broken):        1.49 M ops/s (mmap fallback)
After Phase 5 (fixed):          41.0 M ops/s (+28.9x)
vs System malloc:               26.8 M ops/s (1.53x faster)
```
**Achievement**: ✅ Major success!

### Overall Status
- ✅ **Tiny allocations** (16B-1KB): 52-57 M ops/s (good, some regression)
- ✅ **Mid MT allocations** (1KB-8KB): 41 M ops/s (excellent, 1.53x vs system)
- ⏸️ **Large allocations** (32KB-2MB): Not benchmarked yet
- ⏸️ **MT workloads**: No MT benchmarks yet

---

## Decision Time

**Choose your next phase**:
- **Option A**: Investigate bench_random_mixed regression
- **Option B**: PGO re-enablement (recommended)
- **Option C**: Expand Tiny Front Config Box
- **Option D**: Production readiness & benchmarking
- **Option E**: Multi-threaded optimization

**Or**: Take a break, Phase 5 is a big win! 🎉

---

Updated: 2025-11-29
Phase: 5 COMPLETE → 6 PENDING
Previous: Phase 4 (Tiny Front Optimization, +7.3%)
Achievement: +28.9x Mid MT improvement (1.49M → 41.0M ops/s)