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

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Message-ID: <y0mhbuplmlr.fsf@fche.csb>
Date:	Sat, 26 Sep 2009 12:03:28 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Arjan van de Ven <arjan@...radead.org>
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


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?


- FChE
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