Profiling JVM languages on the roboRIO

[connor.worley]

Last night we were trying to debug some loop overrun issues in our code. Nothing we had written seemed egregiously slow, so I suggested using a profiler to get a better picture of what was happening. It turned out that this was actually possible for JVM languages on the roboRIO!

I did some searching and found async-profiler, which seemed like a reasonable choice. The Linux/ARM binary linked in its README does not work on the roboRIO, so I cross-compiled a working one. You can download it here.

To use the profiler…

• Unzip it and SCP the profiler directory into the ~admin directory on the roboRIO.
• SSH into the admin account on the roboRIO.
• Set the kernel settings as described in async-profiler’s README.
• Find the process ID of your robot code with ps aux | grep java.
• Put the robot into whatever conditions you want to profile (for us, this meant enabling teleop and letting it sit).
• Run the profiler! For some reason it wouldn’t write any output to files, but I was able to get it to output to stdout. Our command looked something like ~/profiler/profiler.sh -i 100us -d 30 -g -o tree <java process id> > ~/profile.html.
• SCP ~admin/profile.html back to your computer for inspection.

Here’s one of the profiles we captured. There’s already some interesting takeaways and items to optimize in there, so I figured this sort of procedure would be useful to share with other teams. Happy optimizing!