C++ Running Instruction

Run your program and acquire a stack trace

Make sure you are in the same directory used above to clone the FlameGraph repository.

1. Have the program to be profiled running.

2. Begin Profiling:

   sudo perf record -F 99 -a -g -- sleep 60

   About this command:

   perf` is the Linux tool for getting kernel stack traces.

   We are running it in record mode

   -F 99 says that we want to gather stacks at a frequency of 99 Hz

   -a says we wil capturing data for all CPUs

   -g says we want call graph (call stack) information

   -- is the separator between options and the command

   sleep 60 says to record data for 60 seconds

   The parameters here that you can tune are the frequency and the time to record. Some CPUs have been know to have trouble at values greater than 100 Hz, so try for 99 Hz and below.

3. Now it’s time to dump the profiling results to a file

   We will also combine this step with collapsing the stacks by frequency

   sudo perf script | ./FlameGraph/stackcollapse-perf.pl > out.perf-folded

   If you see some errors here about “failed to open” or “no symbols found”, that is fine, they are not related to the profiling and relate to some other temporary files.

   The stackcollapse program takes a file with a list of stacks that looks like:

    stack1
    stack2
    stack1
    stack1
    stack2
   

   And then collapses the stacks by frequency to something like:

    3 stack1
    2 stack2
   

   This makes it easier for the FlameGraph tool to assign a size to each stack.

4. Generate the flame graph

   To see the system-wide flame graph use the command:

   ./FlameGraph/flamegraph.pl out.perf-folded > systemWide.svg

   This svg file can be view in the browser using firefox systemWide.svg

   Once you know the reported name of your program (bottom most layer specific to your program), you can filter the stack results with grep. It also may be easier to find your program’s name by clicking on stacks which will zoom the graph to that area and you can see the results more closely.

    grep "MyProgramName" out.perf-folded | ./FlameGraph/flamegraph.pl > myProgramGraph.svg
   

   Similarly, this can be viewed with firefox myProgramGraph.svg

Summary

This is the order of commands to be ran:

1. git clone --depth=1 https://github.com/brendangregg/FlameGraph.git
2. Compile with -g -fno-omit-frame-pointer
3. sudo perf record -F 99 -a -g -- sleep 60
4. sudo perf script | ./FlameGraph/stackcollapse-perf.pl > out.perf-folded

5. grep “MyProgramName” out.perf-folded

   ./FlameGraph/flamegraph.pl > myProgramGraph.svg

6. firefox myProgramGraph.svg

Source

Brendan Gregg’s Website