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SubjectRe: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters
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
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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