From mboxrd@z Thu Jan  1 00:00:00 1970
From: Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH 1/3] perf: add context field to perf_event
Date: Thu, 21 Jul 2011 17:37:57 +0100
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Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>,
	"acme@ghostprotocols.net" <acme@ghostprotocols.net>,
	Jason Wessel <jason.wessel@windriver.com>
To: Avi Kivity <avi@redhat.com>
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On Thu, Jul 21, 2011 at 04:59:00PM +0100, Avi Kivity wrote:
> On 07/21/2011 06:46 PM, Will Deacon wrote:
> > >
> > >  This is (and must be) called from a preempt disabled context, no mutexes
> > >  around here.
> >
> > Bah, yes, that is essential if you're dealing with current. Maybe use a
> > spinlock instead?
> 
> Could work.  Not thrilled about adding it to the kvm hot path, but I 
> can't say it will make a measurable impact.

Understood, but at least it doesn't contribute to finish_task_switch. I also
wouldn't expect to have multiple preempt registrations in parallel for the
same task so that lock should rarely (if ever) be contended.

Will