github.com/elastic/go-perf

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This is a clone of the golang.org/x/sys/unix/linux/perf submitted by acln0 to review at https://go-review.googlesource.com/c/sys/+/168059

An alternative working tree for this package can also be found at https://github.com/acln0/perf

This Elastic fork contains bugfixes and features necessary for our KProbes implementation.

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perf API client package for Linux. See man 2 perf_event_open and include/uapi/linux/perf_event.h.

This package is in its early stages. The API is still under discussion: it may change at any moment, without prior notice. Furthermore, this document may not be completely up to date at all times.

Testing

Many of the things package perf does require elevated privileges on most systems. We would very much like for the tests to not require root to run. Because of this, we use a fairly specific testing model, described next.

If the host kernel does not support perf_event_open(2) (i.e. if the /proc/sys/kernel/perf_event_paranoid file is not present), then tests fail immediately with an error message.

Tests are designed in such a way that they are skipped if their requirements are not met by the underlying system. We would like the test suite to degrade gracefully, under certain circumstances.

For example, when running Linux in a virtualized environment, various hardware PMUs might not be available. In such situations, we would like the test suite to continue running. For this purpose, we introduce the mechanism described next.

Requirements for a test are specified by invoking the requires function, at the beginning of a test function. All tests that call perf_event_open must specify requirements this way. Currently, we use three kinds of requirements:

• perf_event_paranoid values

• the existence of various PMUs (e.g. "cpu", "software", "tracepoint")

• tracefs is mounted, and readable

Today, setting perf_event_paranoid=1 and having a readable tracefs mounted at /sys/kernel/debug/tracing enables most of the tests. A select few require perf_event_paranoid=0. If the test process is running with CAP_SYS_ADMIN, perf_event_paranoid requirements are ignored, since they are considered fulfilled. The test process does not attempt to see if it is running as root, it only checks CAP_SYS_ADMIN.

If you find a test that, when ran without elevated privileges, fails with something akin to a permissions error, then it means the requirements for the test were not specified precisely. Please file a bug. Extending the test suite and making these requirements more precise is an ongoing process.