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)

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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

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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

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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%)

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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

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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

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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)

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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)

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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)

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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

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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

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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! 🎉

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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)