hakmem/docs/analysis/PHASE76_0_C7_STATISTICS_ANALYSIS.md

Phase 76-0: C7 Per-Class Statistics Analysis (SSOT化)

Executive Summary

Definitive C7 Statistics from Mixed SSOT Workload:

• C7 Hit Count: 0 (ZERO allocations)
• C7 Percentage: 0.00% of C4-C7 operations
• Verdict: NO-GO for C7 P2 (inline slots optimization)

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Test Configuration

Binary: bench_random_mixed_hakmem_observe (with HAKMEM_MEASURE_UNIFIED_CACHE=1)

Environment Variables:

HAKMEM_WARM_POOL_SIZE=16
HAKMEM_TINY_C5_INLINE_SLOTS=1
HAKMEM_TINY_C6_INLINE_SLOTS=1

Benchmark Parameters:

• Iterations: 20,000,000
• Working Set Size: 400
• Runs: 1 (per-class stats are cumulative)

Unified Cache Initialization:

C4 capacity = 64  (power of 2)
C5 capacity = 128 (power of 2)
C6 capacity = 128 (power of 2)
C7 capacity = 128 (power of 2)

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Results: Per-Class Statistics

C7 Statistics (CRITICAL FINDING)

Metric	Value
Hit Count	0
Miss Count	0
Push Count	0
Full Count	0
Total Allocations	0
Occupied Slots	0/128
Hit Rate	N/A
Full Rate	N/A

Status: C7 received ZERO allocations in the Mixed SSOT workload.

C4-C7 Ranking (Cumulative)

Class	Hit Count	Miss Count	Capacity	Hit %	Percentage of Total
C6	2,750,854	1	128	100.0%	57.17%
C5	1,373,604	1	128	100.0%	28.55%
C4	687,563	1	64	100.0%	14.29%
C7	0	0	128	N/A	0.00%
TOTAL	4,812,021	3	—	—	100.00%

Coverage Analysis

Cumulative Classes	Operations	Percentage
C6 alone	2,750,854	57.17%
C5+C6	4,124,458	85.72%
C4+C5+C6	4,812,021	100.00%
C4+C5+C6+C7	4,812,021	100.00% (no change)

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Decision Analysis

Threshold Criteria

• GO for C7 P2: C7 > 20% of C4-C7 operations
• NEUTRAL: 15% < C7 ≤ 20% of C4-C7 operations
• CONSIDER C4 redesign: C7 ≤ 15% of C4-C7 operations

Verdict: NO-GO for C7 P2

C7: 0.00% - Falls far below any viable threshold

Explanation:

1. Zero Volume: The Mixed SSOT workload (128-1024B allocations) does NOT generate any C7 (1024-2048B) allocations.
2. Workload Mismatch: The benchmark parameters (400 working set size, 20M iterations) are tuned to exercise C4-C6 intensively but avoid C7 entirely.
3. No Optimization Benefit: Any C7 P2 (inline slots) optimization would provide 0% improvement for this specific workload.
4. Resource Opportunity Cost: Engineering effort for C7 P2 would be better spent on C4 (14.29%) or investigating alternative workloads.

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Recommended Next Phase

Phase 76-1: C4 Per-Class Deep Dive

Objective: Analyze C4 (14.3% of total operations) as the next optimization target

Rationale:

• C4 is the largest remaining bottleneck after C5+C6 inline slots
• C4 (256-512B) represents a significant portion of tiny allocations
• After C5/C6 optimizations (85.7%), C4 becomes critical for overall performance

Investigation Areas:

1. C4 Hit Rate: Currently 100.0% (full cache hits) - room for miss reduction?
2. C4 Cache Occupancy: 63/64 slots occupied (near full)
3. C4 Allocation Pattern: Is there temporal locality opportunity?
4. Alternative: Investigate workloads that DO use C7 (system-level, long-lived objects)

Suggested Implementation Options:

• C4 LIFO optimization (vs current FIFO-like behavior)
• C4 spatial locality improvements
• C4 refill batching (similar to C5/C6)
• Hybrid C4-C5 inline slots strategy

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Artifacts

Raw Log

Location: /tmp/phase76_0_c7_stats.log

Key excerpts:

[Unified-STATS] Unified Cache Metrics:
[Unified-STATS] Consistency Check:
[Unified-STATS]   total_allocs (hit+miss) = 5327287
[Unified-STATS]   total_frees (push+full) = 1202827

  C2: 128/2048 slots occupied, hit=172530 miss=1 (100.0% hit), push=172531 full=0 (0.0% full)
  C3: 128/2048 slots occupied, hit=342731 miss=1 (100.0% hit), push=342732 full=0 (0.0% full)
  C4: 63/64 slots occupied, hit=687563 miss=1 (100.0% hit), push=687564 full=0 (0.0% full)
  C5: 75/128 slots occupied, hit=1373604 miss=1 (100.0% hit), push=0 full=0 (0.0% full)
  C6: 42/128 slots occupied, hit=2750854 miss=1 (100.0% hit), push=0 full=0 (0.0% full)
  [C7 MISSING - 0 operations]

Throughput =  46152700 ops/s [iter=20000000 ws=400] time=0.433s

Verification Output

C7 Initialization: ✓ Capacity=128 allocated
C7 Route Assignment: ✓ LEGACY route configured
C7 Operations: ✗ ZERO allocations
C7 Carve Attempts: 0 (no operations triggered)
C7 Warm Pool: 0 pops, 0 pushes
C7 Meta Used Counter: 0 total operations

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Key Insights

1. Workload Characterization: The Mixed SSOT benchmark is optimized for C4-C6 (128-1024B). This is intentional and appropriate for most mixed workloads.

2. C7 Market Opportunity: C7 (1024-2048B) allocations appear in:

   • Long-lived data structures (hash tables, trees)
   • System-level workloads (networking buffers)
   • Specialized benchmarks (not representative of general use)

3. Optimization Priority:

   • C6 (57.2%): ✓ Already optimized with inline slots
   • C5 (28.5%): ✓ Already optimized with inline slots
   • C4 (14.3%): ← Next optimization target
   • C7 (0.0%): ✗ No presence in mixed workload

4. Engineering Trade-offs:

   • C7 P2 would add complexity for 0% mixed-workload benefit
   • C4 redesign could improve 14.3% of operations
   • Consider phase-out of C7 optimization if isolated workloads don't justify it

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Conclusion

Phase 76-0 Complete: C7 is definitively measured at 0.00% of Mixed SSOT operations.

Next Action: Proceed to Phase 76-1: C4 Analysis to evaluate the largest remaining optimization opportunity (14.29% of total operations).

File: /tmp/phase76_0_c7_stats.log Date: 2025-12-18 Status: ✓ Decision gate established