July 13th-16th, 2010
Ottawa Westin
Ottawa, Canada

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Summary

Using trace-cmd to trace the kernel with Ftrace

Ftrace is the internal kernel tracer that has been in Linux since 2.6.27. The interface to work with Ftrace is through the debug file system. Although Ftrace is fully functional with just using echo, cat and grep, having a tool as a front end becomes much more convenient. A tool is also needed to take advantage of reading the raw binary buffers from the trace to give the ability to capture a magnitude more information than using the ASCII output of trace_pipe.

This tutorial will show how to use trace-cmd, a user space utility, to create a binary file from the Ftrace ring buffers. It can initiate tracing functions, events, and has a full range of filters. It even has the ability to record a trace to another box that is running the trace-cmd listen command, which is ideal for embedded boards with limited disk storage.

If you are still new to Ftrace, a quick tutorial about Ftrace's functionality will be presented before delving into the trace-cmd tool. The Fedora 12 kernel includes all the functionality that is needed for this tutorial. If you are using another distribution, you may need to compile your own kernel and enable all the Ftrace features to get the full experience of trace-cmd. Linux 2.6.32 or later is recommended.

A demo of the up and coming KernelShark (GUI interface to Ftrace) will also be included.

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