linux-kernel - Re: [PATCH 4/4] trace: profile all if conditionals

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Date:	Sun, 23 Nov 2008 22:38:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 4/4] trace: profile all if conditionals


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

> On Sun, 23 Nov 2008, Andi Kleen wrote:
> > Steven Rostedt <rostedt@...dmis.org> writes:
> 
> > > This adds a significant amount of overhead and should only be 
> > > used by those analyzing their system.
> > 
> > Often this can be also done using CPU performance counters. Might 
> > be a cheaper option.
> 
> I'd love to add an option that could hook into any arch with HW 
> support for this. We could dump out the same information, but just a 
> different way to gather it.  But I'm still ignorant to the use of 
> CPU performance counters and how to find which branch matches which 
> if.

there's already new ftrace code for this and the patches are done - 
stay tuned.

but it wont be a replacement for the soft method (which is more 
flexible - the hw can only do 'all or nothing' type of branch 
tracing), so it's complementary.

	Ingo
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