linux-kernel - Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs

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Message-ID: <20110829171155.GD9748@somewhere.redhat.com>
Date:	Mon, 29 Aug 2011 19:11:57 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle
 enter/exit APIs

On Mon, Aug 29, 2011 at 04:25:22PM +0200, Peter Zijlstra wrote:
> 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?

But we can stop the tick from the kernel, not just userspace.
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