The Embedded New Testament

The "Holy Bible" for embedded engineers

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Performance Profiling for Embedded Systems

Understanding performance profiling through concepts, not just code. Learn why performance matters and how to think about system optimization.

📋 Table of Contents

• Concept → Why it matters → Minimal example → Try it → Takeaways
• Core Concepts
• Profiling Techniques
• CPU Profiling
• Memory Profiling
• Timing Profiling
• Guided Labs
• Check Yourself
• Cross-links

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Concept → Why it matters → Minimal example → Try it → Takeaways

Concept: Performance profiling is like being a detective investigating why your embedded system isn’t running as fast or efficiently as it should be. It’s about measuring what’s actually happening rather than guessing.

Why it matters: In embedded systems, performance directly affects battery life, responsiveness, and whether you can meet real-time deadlines. Without profiling, you’re optimizing blindly and might waste time on the wrong things.

Minimal example: A simple LED blinking program that should run every 100ms but sometimes takes 150ms. Profiling reveals that a sensor reading function is occasionally taking too long.

Try it: Start with a simple program and measure its performance, then add complexity and observe how performance changes.

Takeaways: Performance profiling gives you data to make informed decisions about optimization, ensuring you focus on the real bottlenecks rather than perceived problems.

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📋 Quick Reference: Key Facts

Performance Profiling Fundamentals

• Measurement: Systematic analysis of system behavior and resource usage
• Data-Driven: Provides actual performance data instead of guessing
• Non-Intrusive: Minimal impact on system performance during profiling
• Real-Time: Essential for meeting timing requirements in embedded systems
• Resource Optimization: Helps optimize CPU, memory, and power usage

Profiling Techniques

• Instrumentation: Insert timing and measurement code into source
• Sampling: Periodic collection of system state and execution context
• Event-Based: Triggered by specific events or conditions
• Statistical: Statistical analysis of performance data over time

Key Performance Metrics

• CPU Profiling: Function execution time, CPU utilization, call frequency
• Memory Profiling: Allocation patterns, memory leaks, fragmentation
• Timing Profiling: Response time, latency, jitter, deadline compliance
• Power Profiling: Power consumption, efficiency, battery life impact
• I/O Profiling: Peripheral usage, communication bottlenecks

Common Bottlenecks

• I/O Operations: Sensor reading, communication protocols, file operations
• Computational Complexity: Complex algorithms, mathematical calculations
• Memory Access: Cache misses, poor data locality, memory bandwidth
• System Overhead: Context switches, interrupt handling, OS calls
• Resource Contention: Shared resource conflicts, priority inversion

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🧠 Core Concepts

What is Performance Profiling?

Performance profiling is the systematic measurement and analysis of how your system behaves in terms of speed, memory usage, and resource consumption. It’s like having a dashboard that shows you exactly what’s happening under the hood.

┌─────────────────────────────────────────────────────────────┐
│                    Performance Profiling Overview            │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐    │
│  │   System    │───▶│  Profiling  │───▶│   Analysis  │    │
│  │  Running    │    │   Tools     │    │   Results   │    │
│  └─────────────┘    └─────────────┘    └─────────────┘    │
│         │                   │                   │          │
│         ▼                   ▼                   ▼          │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐    │
│  │   CPU Time  │    │  Memory     │    │   Timing    │    │
│  │   Usage     │    │  Usage      │    │   Data      │    │
│  └─────────────┘    └─────────────┘    └─────────────┘    │
│                                                           │
│  The goal: Find bottlenecks and optimization opportunities │
└─────────────────────────────────────────────────────────────┘

Why Profile Instead of Guess?

Guessing Approach:

┌─────────────────────────────────────────────────────────────┐
│                    Guessing vs Profiling                   │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  ❌ Guessing:                                              │
│  "I think the problem is in the sensor reading function"  │
│                                                           │
│  • Spend hours optimizing sensor code                     │
│  • Performance improves by 5%                             │
│  • Real bottleneck was elsewhere                          │
│  • Wasted time and effort                                 │
│                                                           │
│  ✅ Profiling:                                             │
│  "Let me measure where the time is actually spent"        │
│                                                           │
│  • Identify actual bottlenecks                            │
│  • Focus optimization efforts                             │
│  • Measure real improvements                              │
│  • Efficient use of time                                  │
└─────────────────────────────────────────────────────────────┘

Performance Metrics That Matter

Different types of profiling give you different insights:

┌─────────────────────────────────────────────────────────────┐
│                    Performance Metrics                     │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐        │
│  │   CPU       │  │   Memory    │  │   Timing    │        │
│  │ Profiling   │  │ Profiling   │  │ Profiling   │        │
│  └─────────────┘  └─────────────┘  └─────────────┘        │
│                                                           │
│  • Function execution time                                │
│  • CPU utilization                                        │
│  • Call frequency                                         │
│                                                           │
│  • Memory allocation                                      │
│  • Memory leaks                                           │
│  • Fragmentation                                          │
│                                                           │
│  • Response time                                          │
│  • Jitter                                                 │
│  • Deadline compliance                                     │
│                                                           │
│  Each metric tells a different story about performance    │
└─────────────────────────────────────────────────────────────┘

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🔍 Profiling Techniques

Instrumentation vs Sampling

There are two main approaches to profiling:

Instrumentation (Code Insertion):

┌─────────────────────────────────────────────────────────────┐
│                    Instrumentation Profiling               │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  Original Code:                                           │
│  void readSensor() {                                      │
│      sensor_value = read_adc();                           │
│      process_data(sensor_value);                          │
│  }                                                        │
│                                                           │
│  Instrumented Code:                                       │
│  void readSensor() {                                      │
│      uint32_t start_time = get_timer();                   │
│      sensor_value = read_adc();                           │
│      uint32_t adc_time = get_timer() - start_time;        │
│      update_profile("ADC_READ", adc_time);                │
│                                                           │
│      start_time = get_timer();                            │
│      process_data(sensor_value);                          │
│      uint32_t process_time = get_timer() - start_time;    │
│      update_profile("PROCESS", process_time);              │
│  }                                                        │
│                                                           │
│  ✅ Precise measurements                                  │
│  ❌ Code overhead                                         │
│  ❌ Changes program behavior                              │
└─────────────────────────────────────────────────────────────┘

Sampling (Statistical):

┌─────────────────────────────────────────────────────────────┐
│                    Sampling Profiling                     │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐        │
│  │   Timer     │  │   Sample    │  │   Analyze   │        │
│  │  Interrupt  │  │   Current   │  │   Results   │        │
│  └─────────────┘  └─────────────┘  └─────────────┘        │
│                                                           │
│  Every 1ms:                                               │
│  • Check what function is running                          │
│  • Increment counter for that function                     │
│  • Continue normal execution                               │
│                                                           │
│  ✅ Minimal overhead                                      │
│  ✅ No code changes                                       │
│  ❌ Less precise                                          │
│  ❌ May miss short functions                              │
└─────────────────────────────────────────────────────────────┘

When to Use Each Technique

Choose Instrumentation When:

• You need precise timing measurements
• You’re profiling specific functions or code sections
• You can modify the source code
• You need detailed performance data

Choose Sampling When:

• You want minimal impact on system performance
• You’re profiling the entire system
• You can’t modify the source code
• You need a quick overview of performance

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⚡ CPU Profiling

What CPU Profiling Tells You

CPU profiling reveals where your program spends its time:

┌─────────────────────────────────────────────────────────────┐
│                    CPU Profiling Results                   │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  Function Name          │ Calls │ Total Time │ % of Total │
│  ────────────────────────────────────────────────────────── │
│  read_sensor()          │  1000 │     50ms   │    50%     │
│  process_data()         │  1000 │     30ms   │    30%     │
│  send_data()            │   100 │     15ms   │    15%     │
│  main_loop()            │  1000 │      5ms   │     5%     │
│                                                           │
│  Insights:                                               │
│  • read_sensor() is the biggest time consumer            │
│  • process_data() is the second biggest                  │
│  • send_data() is called less but takes significant time │
│  • main_loop() overhead is minimal                       │
│                                                           │
│  Optimization Strategy:                                   │
│  • Focus on read_sensor() first                          │
│  • Then optimize process_data()                          │
│  • Consider batching send_data() calls                   │
└─────────────────────────────────────────────────────────────┘

Common CPU Bottlenecks

I/O Operations:

• Reading sensors, UART, SPI, I2C
• File system operations
• Network communication

Computational Complexity:

• Complex algorithms
• Mathematical calculations
• Data processing loops

Memory Access Patterns:

• Cache misses
• Memory bandwidth limitations
• Poor data locality

System Calls:

• Operating system overhead
• Context switches
• Interrupt handling

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💾 Memory Profiling

What Memory Profiling Reveals

Memory profiling shows how your program uses memory over time:

┌─────────────────────────────────────────────────────────────┐
│                    Memory Usage Over Time                  │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  Memory Usage (bytes)                                     │
│  ┌─────────────────────────────────────────────────────┐   │
│  │                                                     │   │
│  │    ██████████████████████████████████████████████   │   │
│  │   ████████████████████████████████████████████████  │   │
│  │  ██████████████████████████████████████████████████ │   │
│  │  ██████████████████████████████████████████████████ │   │
│  │  ██████████████████████████████████████████████████ │   │
│  │                                                     │   │
│  └─────────────────────────────────────────────────────┘   │
│  ↑           ↑           ↑           ↑                    │
│  0s          10s         20s         30s                  │
│                                                           │
│  ❌ Memory leak detected!                                 │
│  • Memory usage keeps growing                            │
│  • No apparent reason for increase                        │
│  • System will eventually run out of memory              │
└─────────────────────────────────────────────────────────────┘

Memory Profiling Metrics

Allocation Patterns:

• How much memory is allocated
• When memory is allocated and freed
• Memory allocation frequency

Memory Leaks:

• Memory that’s allocated but never freed
• Growing memory usage over time
• Unreachable memory blocks

Fragmentation:

• Small free memory blocks scattered throughout
• Inability to allocate large contiguous blocks
• Wasted memory space

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⏱️ Timing Profiling

Real-Time Performance

In embedded systems, timing is often more critical than raw speed:

┌─────────────────────────────────────────────────────────────┐
│                    Timing Requirements                     │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐        │
│  │   Task A    │  │   Task B    │  │   Task C    │        │
│  │  100ms      │  │  500ms      │  │  1000ms     │        │
│  └─────────────┘  └─────────────┘  └─────────────┘        │
│                                                           │
│  Timing Constraints:                                       │
│  • Task A must complete within 100ms                      │
│  • Task B must complete within 500ms                      │
│  • Task C must complete within 1000ms                     │
│                                                           │
│  Performance Goal:                                         │
│  • Meet all deadlines consistently                        │
│  • Minimize jitter (timing variation)                     │
│  • Predictable response times                             │
└─────────────────────────────────────────────────────────────┘

Jitter Analysis

Jitter is the variation in timing - it’s often more important than average performance:

┌─────────────────────────────────────────────────────────────┐
│                    Jitter Analysis                        │
├─────────────────────────────────────────────────────────────┤
│                                                           │
│  Low Jitter (Good):                                       │
│  ┌─┐  ┌─┐  ┌─┐  ┌─┐  ┌─┐  ┌─┐  ┌─┐  ┌─┐              │
│  │█│  │█│  │█│  │█│  │█│  │█│  │█│  │█│              │
│  └─┘  └─┘  └─┘  └─┘  └─┘  └─┘  └─┘  └─┘              │
│  Consistent 100ms intervals                               │
│                                                           │
│  High Jitter (Bad):                                       │
│  ┌─┐    ┌─┐  ┌─┐      ┌─┐    ┌─┐  ┌─┐                  │
│  │█│    │█│  │█│      │█│    │█│  │█│                  │
│  └─┘    └─┘  └─┘      └─┘    └─┘  └─┘                  │
│  Variable intervals: 80ms, 120ms, 90ms, 130ms            │
│                                                           │
│  High jitter can cause:                                   │
│  • Missed deadlines                                       │
│  • Unpredictable behavior                                 │
│  • System instability                                     │
└─────────────────────────────────────────────────────────────┘

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🧪 Guided Labs

Lab 1: Basic Timing Measurement

Objective: Understand how to measure basic performance.

Setup: Create a simple program that performs a repetitive task.

Steps:

1. Create a function that does some work (e.g., mathematical calculations)
2. Measure how long it takes to execute
3. Run it multiple times and observe timing variations
4. Identify sources of timing variation

Expected Outcome: Understanding of basic timing measurement and the concept of jitter.

Lab 2: Function Profiling

Objective: Learn to profile individual functions.

Setup: Create a program with multiple functions of different complexities.

Steps:

1. Implement simple profiling for each function
2. Run the program and collect timing data
3. Analyze which functions take the most time
4. Identify optimization opportunities

Expected Outcome: Understanding of how to identify performance bottlenecks in code.

Lab 3: Memory Usage Analysis

Objective: Learn to profile memory usage.

Setup: Create a program that allocates and frees memory.

Steps:

1. Implement memory allocation tracking
2. Run the program and monitor memory usage
3. Introduce a memory leak and observe the effect
4. Fix the leak and verify the fix

Expected Outcome: Understanding of memory profiling and leak detection.

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✅ Check Yourself

Understanding Check

• Can you explain why performance profiling is better than guessing?
• Do you understand the difference between instrumentation and sampling?
• Can you explain what CPU profiling tells you?
• Do you understand what memory profiling reveals?
• Can you explain why timing and jitter matter in embedded systems?

Application Check

• Can you implement basic timing measurements in your code?
• Do you know how to profile function execution times?
• Can you track memory allocation and usage?
• Do you understand how to identify performance bottlenecks?
• Can you measure and analyze jitter in your system?

Analysis Check

• Can you choose appropriate profiling techniques for different situations?
• Do you understand how to interpret profiling results?
• Can you prioritize optimization efforts based on profiling data?
• Do you know how to measure the effectiveness of optimizations?
• Can you design a profiling strategy for a complex embedded system?

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🔗 Cross-links

Related Topics

• Real-Time Systems: Understanding real-time performance requirements
• Memory Management: Understanding memory allocation and management
• System Integration: Integrating profiling into the build process
• Performance Optimization: Using profiling data for optimization

Further Reading

• Performance Profiling Tools: Overview of available profiling tools
• Real-Time Performance Analysis: Deep dive into real-time systems
• Memory Profiling Techniques: Advanced memory analysis methods
• Embedded System Optimization: Using profiling for system optimization

Industry Standards

• Real-Time Systems: Industry standards for real-time performance
• Performance Measurement: Standardized approaches to performance analysis
• Embedded System Benchmarks: Industry benchmarks for embedded systems
• Safety-Critical Systems: Performance requirements for safety-critical applications