linux-kernel - Re: [PATCH][GIT PULL] tracing: add function profiler

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Date:	Sat, 21 Mar 2009 17:26:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH][GIT PULL] tracing: add function profiler


* Steven Rostedt <rostedt@...dmis.org> wrote:

> > If you want exact function count profiling we could try to do 
> > something perf counter based, eg. stick a software counter in 
> > the mcount thingy.
> 
> I'd like to get the function graph version working, in order to 
> calculate the times spent in each funtion, then I can see how we 
> can (if possible) convert it over to perf counters. :-/

the perf counters angle is definitely worth pursuing (for 
completeness of the scheme Peter is working on), but please lets not 
throw the baby out with the bath water: in-kernel histogram 
collection has real value.

It's _much_ faster than any user-space counter-part, especially for 
such things as branch tracing or function tracing.

	Ingo
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