Flame Graph

1. perf Command

It is a performance-analysis tool natively provided by Linux. It returns the function name currently being executed by the CPU and the call stack (stack).

1.1. Usage

sudo perf record -F 99 -p 13204 -g -- sleep 30

• perf record means record.
• -F 99 means 99 times per second. If all 99 samples return the same function name, it means the CPU spent this entire second executing the same function, which may indicate a performance problem.
• -p 13204 is the process ID, meaning which process to analyze.
• -g means record the call stack.
• sleep 30 means continue for 30 seconds.

2. Flame Graph

2.1. Why It Exists

Because perf results have poor readability, flame graphs were introduced.

3. What Is a Flame Graph?

A flame graph is an SVG image generated from perf results and is used to display the CPU call stack.

3.1. Example

• The y-axis represents the call stack, with each layer being a function. The deeper the call stack, the taller the flame. The top is the currently executing function, and the functions below are its parent functions.
• The x-axis represents the number of samples. The wider a function is on the x-axis, the more often it was sampled, meaning it executed for longer. Note that the x-axis does not represent time; all call stacks are merged and then arranged alphabetically.
• Interaction
  • Hovering the mouse displays the full function name, the number of samples, and the percentage of total samples it occupies.
  • Clicking a layer horizontally enlarges the flame graph so that the layer occupies the full width and shows detailed information.
  • Pressing Ctrl + F displays a search box. The user can enter a keyword or regular expression, and all matching function names are highlighted.

4. Usage

• pprof.md

5. References

• How to Read a Flame Graph? - Ruan Yifeng’s Weblog