[PATCH 0/4] ftrace - Add function duration tracer to ftrace

[Tim Bird <tim.bird@am.sony.com>]

I've created a new tracer, called the "function duration" tracer,
which is derived from the existing function graph tracer.  The
new feature of this tracer, relative to the function graph tracer,
is that it allows filtering by duration.

The rationale for creating a separate tracer is that some of the
optimizations used for the duration tracer were incompatible with
the function graph tracer.  Specifically, I avoid superfluous
calls to the ring_buffer code, avoiding substantial overhead
penalties.  Also, this tracer is more suitable for use at
bootup time (I have a set of patches pending which adds support
for that, on ARM).

The output format for the tracer is amenable to grep-ing.
That is, the duration is on the same line as the function name.

For details about this, see my presentation from the Japan Linux
Symposium:
http://elinux.org/images/7/70/Measuring-function-duration-with-ftrace-oct-2009.pdf

with more information available at the elinux wiki page:
http://elinux.org/Ftrace_Function_Graph_ARM

Patches to follow.  Thanks.
 -- Tim