linux-kernel - Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts

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Date:	Fri, 22 May 2009 10:16:09 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] perf_counter: optimize context switch between
 identical inherited contexts

On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote:
> Since we don't have individual fds for the counters in a cloned
> context, the only thing that can make two clones of a given parent
> different after they have been cloned is enabling or disabling all
> counters with prctl.  To account for this, we keep a count of the
> number of enabled counters in each context.  Two contexts must have
> the same number of enabled counters to be considered equivalent.

Curious point that.. so prctl() can disable counters it doesn't own.

Shouldn't we instead fix that?

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