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Date: Sun, 27 Sep 2009 00:02:46 +0530
From: "K.Prasad" <prasad@linux.vnet.ibm.com>
To: "Frank Ch. Eigler" <fche@redhat.com>, peterz@infradead.org
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org,
       mingo@elte.hu, Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to
	get to performance counters
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References: <20090925122556.2f8bd939@infradead.org> <y0mhbuplmlr.fsf@fche.csb>
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On Sat, Sep 26, 2009 at 12:03:28PM -0400, 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.

Wouldn't SystemTap be another user that desires support for multiple/all CPU
perf-counters (apart from hw-breakpoints as a potential user)? As Arjan pointed
out, perf's present design would support only a per-CPU or per-task counter;
not both.

Thanks,
K.Prasad