linuxkit/docs/kernel-perf.md

Using the perf utility with LinuxKit

The perf utility is a standard Linux tool to access performance counters, trace events and access various other kernel internals for performance analysis.

The perf utility needs to matched be with the kernel. For recent kernel build, LinuxKit provides a linuxkit/kernel-perf package with a matching tag for each kernel under linuxkit/kernel.

There are a number of ways to use linuxkit/kernel-perf package:

1. Add it to the init section. This adds /usr/bin/perf to the systems' root filesystem. From there it can be

• bind mounted into your container
• accessed via /proc/1/root/usr/bin/perf from with in the getty or ssh container.

2. Add it to you package. If you have a custom package already, you can add linuxkit/kernel-perf as another stage in your package and then copy /usr/bin/perf into the final stage.

The first method is preferable since you need to match with the kernel package tag and that is typically defined in the YAML file. I typically don't add the bind mount since this requires further modification and simply create a symlink in the ssh or getty container:

ln -s /proc/1/root/usr/bin/perf /usr/bin/perf

If you want to use perf you may also want to remove the sysctl container, or alternatively, disable the kernel pointer restriction it enables by default:

echo 0 > /proc/sys/kernel/kptr_restrict

Now, perf is ready to use. The LinuxKit perf package only contains the perf binary, but excludes the detailed help messages or additional scripts. If there is demand, we can add them to the LinuxKit package.