linux-kernel - Re: [PATCH v2][RFC] ftrace: function oprofiler

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Message-ID: <alpine.DEB.1.10.0810260951500.20123@gandalf.stny.rr.com>
Date:	Sun, 26 Oct 2008 09:58:01 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH v2][RFC] ftrace: function oprofiler

On Sun, 26 Oct 2008, Peter Zijlstra wrote:

> On Sat, 2008-10-25 at 20:55 -0400, Steven Rostedt wrote:
> 
> > This is a function profiler to count the number of times a function is hit.
> 
> I have to ask, _why_?
> 
> It seems like a nice enough gimmick, but is this information actually
> useful?

Well, it does let you know for sure which functions are the hottest paths.
Perhaps you have a "slow path" function. This will show you how slow
that slow path is. That is, how many times it is hit compared to the
fast path.

With dynamic ftrace, you can also pick and choose which functions
are to be counted.

What is also nice about it (and something that I will use it for), is that
it will show you the functions that will be hit the most during a trace. 
If you do not care about those functions, then you can easily filter them 
out for your trace.

This patch is also a proof of concept. I'm sure others can think of more 
useful things to do by adding more stuff to this patch.

-- Steve

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