PERF & FLAME GRAPH INSTRuCTIONS

Flame Graph provides visual performance analysis, presented in SVG format, supports zooming, and can quickly locate CPU performance bottlenecks. Flame Graph统计了采样周期内，code-path被执行的时间比例，纵轴是code-path，从下至上一般就是call stack。横轴是某个stack的占用时间，跨度越大说明其占CPU比重越高，也就是最耗费CPU的，stack在横轴上是按照字母序排列的，颜色深浅仅仅是为了区分，并没特殊意义。

The following is the Flame Graph generation process:

Use perf to get system execution status
- Step 1：Execute perf record on EVB
```
# ./perf record -a -g sleep 10

-a : CPU

-o : Specify the output file, if not, it will be automatically saved in the current directory, named perf.data

-g : Record call stack

sleep : Specify the duration. Unit: second
```
  If it displays during execution, it means that the system lacks GCC runtime library, please put libgcc_s.so.1 under /mnt or other path, and add it to LD_LIBRARY_PATH.
```
# export LD_LIBRARY_PATH=/mnt:/lib
```
- Step 2：Execute perf report to analyze the saved data
```
# ./perf report
```
  Display the call stack and running time ratio of each leaf function directly on the console.
  
  If FlameGraph analysis is performed directly, perf report is not necessary.
Use data to generate flame graphs
- Step 1：Execute perf script on EVB to parse the data and archive the output result to p1
```
# ./perf script -i perf.data > p1
```
- Step 2：Switch to PC, click to get FlameGraph, execute stackcollapse-perf provided by FlameGraph on PC to fold the symbols of p1 and save it to disk
```
# stackcollapse-perf.pl p1 &> perf.folder
```
- Step 3：Execute p1 provided by FlameGraph on the PC to convert perf.folder to svg, which can be opened with a browser (Chrome or Firefox is recommended)
```
# flamegraph.pl perf.folder > perf.svg
```
  Generate Flame Graph command:
```
./perf record -a -g -F 2599 -p 451 sleep 30
./perf script -i perf.data > p1
./stackcollapse-perf.pl p1 &> perf.folder
./flamegraph.pl perf.folder > perf.svg
```

Reference：

https://www.jianshu.com/p/9a597ff4f5de

https://linux.cn/article-4670-1.html