linux-kernel - Re: [PATCH 4/4] ftrace - function

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Message-ID: <1260416840.2146.134.camel@gandalf.stny.rr.com>
Date:	Wed, 09 Dec 2009 22:47:20 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 4/4] ftrace - function_duration Documentation

On Wed, 2009-12-09 at 14:42 -0800, Tim Bird wrote:
> Documentation for function_duration tracer.

> +The purpose of the function duration tracer is to help find the
> +longest-running, most time-consuming functions in the Linux kernel.
> +This is especially important for early initialization, to reduce
> +kernel boot time.
> +
> +Function duration tracing uses the ftrace ability to hook both the
> +entry and exit of a function, to record duration information for
> +kernel functions.  This is similar to the function_graph tracer, but
> +the function_duration tracer is specially written to support filtering
> +by duration and decreased tracer overhead while filtering.
> +
> +This extends the amount of time that a trace can cover, and reduces
> +interference with the timing of the traced activity.

BTW, have you taken a look at the function profiler? It also keeps track
of all durations without using the ring buffer. It just adds them up and
gives an average time.

-- Steve



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