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

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Date:	Thu, 10 Dec 2009 13:21:52 -0800
From:	Tim Bird <tim.bird@...sony.com>
To:	"rostedt@...dmis.org" <rostedt@...dmis.org>
CC:	"Bird, Tim" <Timothy.Bird@...sony.com>,
	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

Steven Rostedt wrote:
> 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.

I haven't, but I should.  However, my tool has some other options
(like subtracting time spent in interrupts) that I don't
think the profile approach currently supports.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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