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Date:	Fri, 19 Sep 2014 01:17:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v2 1/2] sched: let the scheduler see CPU idle states

On Thu, Sep 18, 2014 at 02:32:25PM -0400, Nicolas Pitre wrote:
> On Thu, 18 Sep 2014, Paul E. McKenney wrote:

> > So what is it that you really need to do here?
> 
> In short, we don't want the cpufreq data to go away (see the 2 scenarios 
> above) while the scheduler is looking at it.  The scheduler uses the 
> provided accessors (see patch 2/2) so we can put any protection 
> mechanism we want in them.  A simple spinlock could do just as well 
> which should be good enough.

rq->lock disables interrupts so on that something like
kick_all_cpus_sync() will guarantee what you need --
wake_up_all_idle_cpus() will not.
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