linux-kernel - Re: [RFC PATCH 05/15] nohz_task: Restart the tick when another task compete on the cpu

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Message-ID: <20101220233857.GC1715@nowhere>
Date:	Tue, 21 Dec 2010 00:39:01 +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 05/15] nohz_task: Restart the tick when another
 task compete on the cpu

On Mon, Dec 20, 2010 at 04:53:21PM +0100, Peter Zijlstra wrote:
> On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> > +#ifdef CONFIG_NO_HZ_TASK
> > +       /*
> > +        * CHECKME:
> > +        * Ideally, we need to check if the target has a nohz task
> > +        * and only send the IPI if so. But there is nothing but
> > +        * a racy way to do that. Or can we assume at that point
> > +        * of the wake up that if cpu_has_nohz_task(cpu) is 0, then
> > +        * it's ok, even if it has a task about to switch to nohz
> > +        * task mode?
> > +        */
> > +       if (rq->nr_running == 2)
> > +               smp_send_update_nohz_task_cpu(cpu);
> > +#endif 
> 
> This is the wrong place, use ttwu_activate(), since activate_task() is
> the thing that pokes at nr_running.

Ok, will do.

Thanks.
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