linux-kernel - Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move perf on top of TP

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Date:	Mon, 10 May 2010 15:20:56 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...e.hu,
	efault@....de, avi@...hat.com, acme@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCHSET] sched,perf: unify tracers in sched and move
 perf on top of TP

On Wed, May 05, 2010 at 11:54:52AM +0200, Tejun Heo wrote:

> On 05/05/2010 11:51 AM, Peter Zijlstra wrote:
> >> I was wondering the other way around - ie. the possibility to make
> >> perf optional and maybe even as a module which depends on TPs, which
> >> would be nicer than the current situation and make the code less
> >> cluttered too. 
> > 
> > I really really hate making perf rely on tracepoints.
> 
> Hmmm.... may I ask why?  Unifying hooking mechanism seems like a good
> idea to me and it's not like it's gonna add any runtime overhead
> although it does complicate init/exit but well that's something you
> have to pay if you wanna do things dynamically and sans the ifdef
> stuff it's like a couple hundred lines of isolated code.

Don't forget where perf_events started out - as a way to count and
record hardware events.  So perf_events is very useful even in a
kernel that has no tracing infrastructure configured in at all. 

Paul.
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