axiom-performance-profiling

# Performance Profiling

## Overview

iOS app performance problems fall into distinct categories, each with a specific diagnosis tool. This skill helps you **choose the right tool**, **use it effectively**, and **interpret results correctly** under pressure.

**Core principle**: Measure before optimizing. Guessing about performance wastes more time than profiling.

**Requires**: Xcode 15+, iOS 14+
**Related skills**: `axiom-swiftui-performance` (SwiftUI-specific profiling with Instruments 26), `axiom-memory-debugging` (memory leak diagnosis)

## When to Use Performance Profiling

#### Use this skill when
- ✅ App feels slow (UI lags, loads take 5+ seconds)
- ✅ Memory grows over time (Xcode shows increasing memory usage)
- ✅ Battery drains fast (device gets hot, battery depletes in hours)
- ✅ You want to profile proactively (before users complain)
- ✅ You're unsure which Instruments tool to use
- ✅ Profiling results are confusing or contradictory

#### Use `axiom-memory-debugging` instead when
- Investigating specific memory leaks with retain cycles
- Using Instruments Allocations in detail mode

#### Use `axiom-swiftui-performance` instead when
- Analyzing SwiftUI view body updates
- Using SwiftUI Instrument specifically

## Performance Decision Tree

Before opening Instruments, narrow down what you're actually investigating.

### Step 1: What's the Symptom?

```
App performance problem?
├─ App feels slow or lags (UI interactions stall, scrolling stutters)
│  └─ → Use Time Profiler (measure CPU usage)
├─ Memory grows over time (Xcode shows increasing memory)
│  └─ → Use Allocations (measure object creation)
├─ Data loading is slow (parsing, database queries, API calls)
│  └─ → Use Core Data instrument (if using Core Data)
│  └─ → Use Time Profiler (if it's computation)
└─ Battery drains fast (device gets hot, depletes in hours)
   └─ → Use Energy Impact (measure power consumption)
```

### Step 2: Can You Reproduce It?

**YES** – Use Instruments to measure it (profil