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

From: Arjan van de Ven <arjan@infradead.org>
To: fche@redhat.com (Frank Ch. Eigler)
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
	peterz@infradead.org, Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters
Date: Sat, 26 Sep 2009 18:11:49 +0200	[thread overview]
Message-ID: <20090926181149.6e5827db@infradead.org> (raw)
In-Reply-To: <y0mhbuplmlr.fsf@fche.csb>

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

> 
> Arjan van de Ven <arjan@infradead.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
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