linux-kernel - Re: [RFC PATCH 14/15] nohz_task: Clear nohz task attribute on exit()

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Message-ID: <20101221142223.GH1750@nowhere>
Date:	Tue, 21 Dec 2010 15:22:25 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 14/15] nohz_task: Clear nohz task attribute on
 exit()

On Tue, Dec 21, 2010 at 09:07:45AM +0100, Peter Zijlstra wrote:
> On Tue, 2010-12-21 at 02:48 +0100, Frederic Weisbecker wrote:
> > On Mon, Dec 20, 2010 at 05:30:28PM +0100, Peter Zijlstra wrote:
> > > On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> > > > 
> > > > Clear the nohz task attribute when a task exits, clear the cpu
> > > > mask and restart the tick if necessary.
> > > > 
> > > I'm not quite sure this all makes sense, I mean, we're going from 1 to 0
> > > tasks, right?
> > 
> > Not necessarily, other tasks can be on the runqueue while that nohz task
> > exits, or we can be alone in which case the tick might be stopped and
> > we need to restart it because rq->nr_running > 1 won't make much sense
> > anymore without the nohz task and if a new task gets enqueued, the tick
> > won't restart until a second one gets in.
> 
> Urgh, so that mask is set even if you're not currently in that mode?
> That's 'interesting'..

I don't get what you mean.
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