# 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)**

---

## Test Configuration

**Binary**: `bench_random_mixed_hakmem_observe` (with HAKMEM_MEASURE_UNIFIED_CACHE=1)

**Environment Variables**:
```bash
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)
```

---

## 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) |

---

## 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.

---

## 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

---

## 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
```

---

## 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

---

## 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