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Subject: Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to
 idle enter/exit APIs
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Anton Blanchard <anton@au1.ibm.com>, Avi Kivity <avi@redhat.com>,
        Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Paul Menage <menage@google.com>,
        Stephen Hemminger <shemminger@vyatta.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Pepper <lnxninja@linux.vnet.ibm.com>
Date: Mon, 29 Aug 2011 16:25:22 +0200
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On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote:
> To prepare for nohz / idle logic split, pull out the rcu dynticks
> idle mode switching to strict idle entry/exit areas.
> 
> So we make the dyntick mode possible without always involving rcu
> extended quiescent state. 

Why is this a good thing? I would be thinking that if we're a userspace
bound task and we disable the tick rcu would be finished on this cpu and
thus the extended quiescent state is just what we want?