linux-kernel - Re: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters

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Message-ID: <20090926181149.6e5827db@infradead.org>
Date:	Sat, 26 Sep 2009 18:11:49 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	fche@...hat.com (Frank Ch. Eigler)
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, peterz@...radead.org,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to
 get to performance counters

On Sat, 26 Sep 2009 12:03:28 -0400
fche@...hat.com (Frank Ch. Eigler) wrote:

> 
> Arjan van de Ven <arjan@...radead.org> writes:
> 
> > [...]
> > There are reasons for kernel code to ask for, and use, performance
> > counters. For example, in CPU freq governors this tends to be a
> > good idea, but there are other examples possible as well of course.
> > 
> > This patch adds the needed bits to do enable this functionality;
> > they have been tested in an experimental cpufreq driver that I'm
> > working on, and the changes are all that I needed to access
> > counters properly. [...]
> 
> For what it's worth, this sort of thing also looks useful from
> systemtap's point of view.
> 
> It appears that the patch assumes that a perf counter instance is to
> be associated with the "current" task.  How do you use this from your
> prototype scheduler?  Do you create/attach a new one for each thread?
> 

your appearance is not correct. A perf counter is either attached to a
task, or to a cpu. I use the later.


--
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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