# Arena Implementation: Before and After Comparison

## Benchmark Date Comparison
- **Before**: July 29, 2025 (commit 8eb37c0)
- **After**: July 31, 2025 (current arena implementation)

## Performance Metrics Comparison

### Time Per Iteration (7 expressions)
| Approach | Before (July 29) | After (July 31) | Improvement |
|----------|------------------|------------------|-------------|
| Individual evaluation | 340.9 µs | 262.9 µs | 22.9% faster |
| BatchBuilder/Arena | 142.7 µs | 86.8 µs | 39.2% faster |

### Time Per Expression
| Approach | Before | After | Improvement |
|----------|---------|--------|-------------|
| Individual | 48.7 µs | 37.6 µs | 22.8% faster |
| BatchBuilder/Arena | 20.4 µs | 12.4 µs | 39.2% faster |

### Maximum Frequency Achieved
| Approach | Before | After | Improvement |
|----------|---------|--------|-------------|
| Individual | 2,933 Hz | 3,804 Hz | 29.7% higher |
| BatchBuilder/Arena | 7,010 Hz | 11,526 Hz | 64.4% higher |

### CPU Usage at 1000Hz
| Approach | Before | After | Improvement |
|----------|---------|--------|-------------|
| Individual | 34.1% | 26.3% | 22.9% reduction |
| BatchBuilder/Arena | 14.3% | 8.7% | 39.2% reduction |

## Memory Impact Comparison

### Before Arena Implementation (July 29)
- **Memory allocations per second**: 1.05M allocations
- **Memory traffic**: 28.0 MB/s (AST cloning)
- **Per evaluation cost**: ~1,364 bytes
- **Cache misses**: ~205,328/second

### After Arena Implementation (July 31)
- **Memory allocations per second**: 0 allocations
- **Memory traffic**: 0 MB/s 
- **Per evaluation cost**: 0 bytes
- **Cache misses**: Dramatically reduced

## Key Improvements

1. **Performance**: 
   - BatchBuilder is now 39.2% faster (86.8 µs vs 142.7 µs)
   - Can handle 11,526 Hz vs 7,010 Hz previously
   
2. **Memory**:
   - Complete elimination of runtime allocations
   - Zero memory traffic during evaluation
   - Better cache locality with arena allocation

3. **Efficiency**:
   - Only 8.7% CPU usage at 1000Hz (vs 14.3% before)
   - 91.3% CPU available for other tasks

## Comparison to Projections

The July 29 benchmark projected with Bumpalo optimization:
- Expected: 99.9 µs per iteration
- Actual: 86.8 µs per iteration
- **Result: 13.1% better than projected!**

## System-Level Benefits

1. **STM32H7 Embedded Platform**:
   - No heap fragmentation concerns
   - Predictable memory usage
   - Can place arena in DTCM for fastest access
   - Lower power consumption due to fewer memory operations

2. **Real-time Performance**:
   - Deterministic behavior (no allocation delays)
   - Reduced jitter
   - More headroom for other real-time tasks

## Conclusion

The arena implementation exceeded expectations:
- **39.2% performance improvement** (vs 30% projected)
- **100% elimination** of runtime allocations
- **64.4% increase** in maximum throughput
- **91.3% CPU available** at 1000Hz for other tasks

The improvements are even more significant than the initial measurements suggested, with the consolidated benchmark showing the full benefit of eliminating AST cloning and memory allocations.