Subject: Re: [PATCH 4/4] ftrace - function_duration Documentation
From: Steven Rostedt <rostedt@goodmis.org>
Reply-To: rostedt@goodmis.org
To: Tim Bird <tim.bird@am.sony.com>
Cc: linux kernel <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
       Frederic Weisbecker <fweisbec@gmail.com>
In-Reply-To: <4B2027C7.9010509@am.sony.com>
References: <4B2027C7.9010509@am.sony.com>
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Organization: Kihon Technologies Inc.
Date: Wed, 09 Dec 2009 22:47:20 -0500
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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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