linux-kernel - Re: [PATCH 3/3] nohz: Use IPI implicit full barrier against rq->nr

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Message-ID: <20140514113852.GB1278@localhost.localdomain>
Date:	Wed, 14 May 2014 13:38:56 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 3/3] nohz: Use IPI implicit full barrier against
 rq->nr_running r/w

On Wed, May 14, 2014 at 11:09:03AM +0200, Peter Zijlstra wrote:
> On Wed, May 14, 2014 at 12:25:56AM +0200, Frederic Weisbecker wrote:
> > @@ -670,10 +670,11 @@ bool sched_can_stop_tick(void)
> >  
> >         rq = this_rq();
> >  
> > -       /* Make sure rq->nr_running update is visible after the IPI */
> > -       smp_rmb();
> > -
> > -       /* More than one running task need preemption */
> > +       /*
> > +	* More than one running task need preemption.
> > +	* nr_running update is assumed to be visible
> > +	* after IPI is sent from wakers.
> > +	*/
> >         if (rq->nr_running > 1)
> >                 return false;
> 
> Looks like whitespace damage on that comment's indenting.

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