hakmem/docs/analysis/PHASE7_COMPREHENSIVE_BENCHMARK_RESULTS.md

Phase 7 Comprehensive Benchmark Results

Date: 2025-11-08 Build Configuration: HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1 Status: CRITICAL BUGS FOUND - NOT PRODUCTION READY

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Executive Summary

Production Readiness: FAILED

Critical Issues Found:

1. Multi-threaded crash: Larson 2T/4T fail with free(): invalid pointer (Exit 134)
2. 64B allocation crash: Bus error (Exit 135) on 64-byte allocations
3. Debug output in production: "Phase 7: tiny_alloc(1024) rejected" messages indicate incomplete implementation

Performance (Single-threaded, working sizes):

• Single-thread performance is excellent (76-120% of System malloc)
• But crashes make this unusable in production

Key Findings

Category	Result	Status
Larson 1T	2.76M ops/s	✅ PASS
Larson 2T/4T	CRASH (Exit 134)	❌ CRITICAL FAIL
Random Mixed (most sizes)	60-72M ops/s	✅ PASS
Random Mixed 64B	CRASH (Bus Error 135)	❌ CRITICAL FAIL
Stability (1M iterations)	Stable scores	✅ PASS
Overall Production Ready	NO	❌ FAIL

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Detailed Benchmark Results

1. Larson Multi-Thread Stress Test

Threads	HAKMEM Result	System Result	Status
1T	2,758,490 ops/s	~3.3M ops/s (est.)	✅ 84% of System
2T	CRASH (Exit 134)	N/A	❌ CRITICAL
4T	CRASH (Exit 134)	N/A	❌ CRITICAL

Crash Details:

[DEBUG] Phase 7: tiny_alloc(1024) rejected, using malloc fallback
free(): invalid pointer
Exit code: 134 (SIGABRT - double free or corruption)

Root Cause: Unknown - likely race condition in multi-threaded free path or malloc fallback integration issue.

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2. Random Mixed Allocation Benchmark

Test: 100,000 iterations of mixed malloc/free patterns

Size	HAKMEM (ops/s)	System (ops/s)	HAKMEM %	Status
16B	66,878,359	87,810,575	76.1%	✅
32B	69,730,339	64,490,458	108.1%	✅
64B	CRASH (Bus Error 135)	78,147,467	N/A	❌ CRITICAL
128B	72,090,413	65,960,798	109.2%	✅
256B	71,363,681	71,688,134	99.5%	✅
512B	60,501,851	62,967,613	96.0%	✅
1024B	63,229,630	67,220,203	94.0%	✅
2048B	55,868,013	46,557,492	119.9%	✅
4096B	40,585,997	45,157,552	89.8%	✅
8192B	35,442,103	33,984,326	104.2%	✅

Performance Highlights (working sizes):

• 32B: +8% faster than System (108.1%)
• 128B: +9% faster than System (109.2%)
• 2048B: +20% faster than System (119.9%)
• 8192B: +4% faster than System (104.2%)

64B Crash Details:

Exit code: 135 (SIGBUS - unaligned memory access or invalid pointer)
Crash during allocation, not free

Root Cause: Unknown - possibly alignment issue or class index calculation error for 64B size class.

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3. Long-Run Stability Tests

Test: 1,000,000 iterations (10x normal) to check for memory leaks and variance

Size	Throughput (ops/s)	Variance vs 100K	Status
128B	72,829,711	+1.0%	✅ Stable
256B	72,305,587	+1.3%	✅ Stable
1024B	64,240,186	+1.6%	✅ Stable

Analysis:

• Variance <2% indicates stable performance
• No memory leaks detected (throughput would degrade if leaking)
• Scores slightly higher in long runs (likely cache warmup effects)

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4. Comparison vs Phase 6 Baseline

Phase 6 Baseline (from CLAUDE.md):

• Tiny: 52.59 M/s (38.7% of System 135.94 M/s)
• Phase 6 Goal: 85-92% of System

Phase 7 Results (working sizes):

• Tiny (128B): 72.09 M/s (109% of System 65.96 M/s) → +37% improvement
• Tiny (256B): 71.36 M/s (99.5% of System) → +36% improvement
• Mid (2048B): 55.87 M/s (120% of System) → Exceeds System by +20%

Goal Achievement:

• Target: 85-92% of System → Achieved 96-120% (working sizes)
• But: Critical crashes make this irrelevant

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5. Comprehensive Benchmark (Phase 8 features)

Status: Could not run - linking errors

Issue: bench_comprehensive.c calls Phase 8 functions:

• hak_tiny_print_memory_profile()
• hkm_learner_init()
• superslab_ace_print_stats()

These are not compatible with Phase 7 build. Would need:

• Remove Phase 8 dependencies, OR
• Build with Phase 8 flags, OR
• Use simpler benchmark suite

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Root Cause Analysis

Issue 1: Multi-threaded Crash (Larson 2T/4T)

Symptoms:

• Single-threaded works perfectly (2.76M ops/s)
• 2+ threads crash immediately with "free(): invalid pointer"
• Consistent across 2T and 4T tests

Debug Output:

[DEBUG] Phase 7: tiny_alloc(1024) rejected, using malloc fallback

Hypotheses:

1. Race condition in TLS initialization: Multiple threads accessing uninitialized TLS
2. Malloc fallback bug: Mixed HAKMEM/libc allocations causing double-free
3. Free path ownership bug: Wrong allocator freeing blocks from the other

Priority: CRITICAL - must fix before any production use

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Issue 2: 64B Bus Error Crash

Symptoms:

• Bus error (SIGBUS) on 64-byte allocations
• All other sizes (16, 32, 128, 256, ..., 8192) work fine
• Crash happens during allocation, not free

Hypotheses:

1. Class index calculation error: 64B might map to wrong class
2. Alignment issue: 64B blocks not aligned to required boundary
3. Header corruption: Class index stored in header (HEADER_CLASSIDX=1) might overflow for 64B

Clue: Debug message shows "tiny_alloc(1024) rejected" even for 64B allocations, suggesting routing logic is broken.

Priority: CRITICAL - 64B is a common allocation size

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Issue 3: Debug Output in Production Build

Symptom:

[DEBUG] Phase 7: tiny_alloc(1024) rejected, using malloc fallback

Impact:

• Performance overhead (fprintf in hot path)
• Indicates incomplete implementation (rejections shouldn't happen in production)
• Suggests Phase 7 optimizations have broken size routing

Priority: HIGH - indicates deeper implementation issues

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Production Readiness Assessment

Success Criteria (from CURRENT_TASK.md)

Criterion	Result	Status
✅ All benchmarks complete without crashes	❌ 2T/4T Larson crash, 64B crash	FAIL
✅ Tiny performance: 85-92% of System	✅ 96-120% (working sizes)	PASS
✅ Mid-Large performance: maintained	✅ 120% of System	PASS
✅ Multi-thread stability: no regression	❌ Complete crash	FAIL
✅ Fragmentation stress: acceptable	⚠️ Not tested (build issues)	SKIP
✅ Comprehensive report generated	✅ This document	PASS

Overall: FAIL - 2 critical crashes

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Recommended Next Steps

Immediate Actions (Critical Bugs)

1. Fix Multi-threaded Crash (Highest Priority)

# Debug with ASan
make clean
make HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1 \
  ASAN=1 larson_hakmem
./larson_hakmem 2 8 128 1024 1 12345 2

# Check TLS initialization
grep -r "PREWARM_TLS" core/
# Verify all TLS variables are initialized before thread spawn

Expected Root Cause: TLS prewarm not actually executing, or race in initialization.

2. Fix 64B Bus Error (High Priority)

# Add debug output to class index calculation
# File: core/box/hak_alloc_api.inc.h or similar
printf("tiny_alloc(%zu) -> class %d\n", size, class_idx);

# Check alignment
# File: core/hakmem_tiny_superslab.c
assert((uintptr_t)ptr % 64 == 0);  // 64B must be 64-byte aligned

Expected Root Cause: HEADER_CLASSIDX=1 storing wrong class index for 64B.

3. Remove Debug Output

# Find and remove/disable debug prints
grep -r "DEBUG.*Phase 7" core/
# Should be gated by #ifdef HAKMEM_DEBUG

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Phase 7 Feature Regression Test

Before deploying any fix, verify:

1. All single-threaded benchmarks still pass
2. Performance doesn't regress to Phase 6 levels
3. No new crashes introduced

Test Suite:

# Single-thread (must pass)
./larson_hakmem 1 1 128 1024 1 12345 1  # Expect: 2.76M ops/s
./bench_random_mixed_hakmem 100000 128 1234567  # Expect: 72M ops/s

# Multi-thread (currently fails, must fix)
./larson_hakmem 2 8 128 1024 1 12345 2  # Expect: no crash
./larson_hakmem 4 8 128 1024 1 12345 4  # Expect: no crash

# 64B (currently fails, must fix)
./bench_random_mixed_hakmem 100000 64 1234567  # Expect: no crash, ~70M ops/s

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Alternate Path: Revert Phase 7 Optimizations

If bugs are too complex to fix quickly:

# Revert to Phase 6
git checkout HEAD~3  # Or specific Phase 6 commit

# Verify Phase 6 still works
make clean && make larson_hakmem
./larson_hakmem 4 8 128 1024 1 12345 4  # Should work

# Incrementally re-apply Phase 7 optimizations
git cherry-pick <HEADER_CLASSIDX commit>  # Test
git cherry-pick <AGGRESSIVE_INLINE commit>  # Test
git cherry-pick <PREWARM_TLS commit>  # Test
# Identify which commit introduced the bugs

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Build Information

Compiler: gcc with LTO Flags:

-O3 -flto -march=native -mtune=native
-DHAKMEM_TINY_PHASE6_BOX_REFACTOR=1
-DHAKMEM_TINY_FAST_PATH=1
-DHAKMEM_TINY_HEADER_CLASSIDX=1
-DHAKMEM_TINY_AGGRESSIVE_INLINE=1
-DHAKMEM_TINY_PREWARM_TLS=1

Known Issues:

• bench_comprehensive won't link (Phase 8 dependencies)
• bench_fragment_stress not tested (same issue)
• Debug output leaking into production builds

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Appendix: Full Benchmark Output Samples

Larson 1T (Success)

=== LARSON 1T BASELINE ===
Throughput =  2758490 operations per second, relative time: 362.517s.
Done sleeping...
[ELO] Initialized 12 strategies (thresholds: 512KB-32MB)
[Batch] Initialized (threshold=8 MB, min_size=64 KB, bg=on)
[ACE] ACE disabled (HAKMEM_ACE_ENABLED=0)

Larson 2T (Crash)

[DEBUG] Phase 7: tiny_alloc(1024) rejected, using malloc fallback
free(): invalid pointer
Exit code: 134

64B Crash

[SUPERSLAB_INIT] class 7 slab 0: usable_size=63488 block_size=1024 capacity=62
[SUPERSLAB_INIT] Expected: 63488 / 1024 = 62 blocks
Exit code: 135 (SIGBUS)

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Conclusion

Phase 7 achieved exceptional single-threaded performance (96-120% of System malloc), but introduced critical bugs:

1. Multi-threaded crash: Unusable with 2+ threads
2. 64B crash: Unusable for common allocation size
3. Incomplete implementation: Debug fallbacks in production code

Recommendation: DO NOT DEPLOY to production. Revert to Phase 6 or fix critical bugs before proceeding to Phase 7 Tasks 6-9.

Next Steps (in priority order):

1. Fix multi-threaded crash (blocker for all production use)
2. Fix 64B bus error (blocker for most workloads)
3. Remove debug output (quality/performance issue)
4. Re-run comprehensive validation
5. Only then proceed to Phase 7 Tasks 6-9

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Generated: 2025-11-08 Test Duration: ~2 hours Total Benchmarks: 15 tests (10 sizes × random mixed, 3 × Larson, 3 × stability) Crashes Found: 2 critical (Larson MT, 64B) Production Ready: ❌ NO