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Ftrace - Steven Rostedt

Biography

Steven Rostedt has been hacking on the Linux kernel since 1999. His main focus is on real-time, but has been becoming more involved with mainline Linux. He developed ftrace based on the work of Ingo Molnar's and William Irwin III's latency tracer that was developed for the -rt patch as well as his own logdev which he wrote back in 1999 when he first started kernel hacking.

Abstract

Ftrace, that has been pulled into the latest git tree and is on track to be in 2.6.27 also comes with an added utility: The dynamic function tracer. This uses the gcc profiling parameter -pg to add a function call at every function inside the kernel. The dynamic utility, converts these calls at runtime to nops, and saves the result. This allows for selective tracing of functions inside the kernel as well as modules. By converting the function calls to nops, and enabling them for tracing, there is no overhead to having a tracer compiled into the kernel. The overhead only appears when the tracer is activated. This means that kernel function tracers may now be enabled in a production environment.

This presentation will lead to a discussion on how to share this code with other projects going on with the kernel, such as LTTng and SystemTap. This is not limited to just tracers, but also for profilers, and for tuning.