linux-kernel - Re: [PATCH 20/22] sched: Move the second half of ttwu() to the remote cpu

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Message-ID: <1300264340.2250.75.camel@laptop>
Date:	Wed, 16 Mar 2011 09:32:20 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	frank.rowand@...sony.com
Cc:	Chris Mason <chris.mason@...cle.com>,
	"Rowand, Frank" <Frank_Rowand@...yusa.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 20/22] sched: Move the second half of ttwu() to the
 remote cpu

On Thu, 2011-03-10 at 17:44 -0800, Frank Rowand wrote:
> > @@ -6287,6 +6342,7 @@ migration_call(struct notifier_block *nf
> >  
> >  #ifdef CONFIG_HOTPLUG_CPU
> >       case CPU_DYING:
> 
> Should pi_lock be locked here, so that additional wake ups can not
> be put on the wake list in the window after sched_ttwu_pending()
> completes, and before set_rq_offline(rq) is called?  If so, then
> of course unlock pi_lock after the matching
> "raw_spin_unlock_irqrestore(&rq->lock, flags);"

The cpu should be offline already, so select_task_rq() will never return
it and hence no new tasks should end up on this list.

> > +             sched_ttwu_pending();
> >               /* Update our root-domain */ 

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