linux-kernel - Re: [RFC][PATCH 08/17] sched: Drop the rq argument to sched_class::select_task

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Message-ID: <1294146052.2016.136.camel@laptop>
Date:	Tue, 04 Jan 2011 14:00:52 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.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>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 08/17] sched: Drop the rq argument to
 sched_class::select_task_rq()

On Tue, 2011-01-04 at 13:59 +0800, Yong Zhang wrote:
> On Mon, Jan 3, 2011 at 7:16 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Wed, 2010-12-29 at 22:31 +0800, Yong Zhang wrote:
> >> On Fri, Dec 24, 2010 at 01:23:46PM +0100, Peter Zijlstra wrote:
> >> > In preparation of calling select_task_rq() without rq->lock held, drop
> >> > the dependency on the rq argument.
> >> >
> >> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >> > ---
> >> > @@ -3416,27 +3409,22 @@ void sched_exec(void)
> >> >  {
> >> >     struct task_struct *p = current;
> >> >     unsigned long flags;
> >> > -   struct rq *rq;
> >> >     int dest_cpu;
> >> >
> >> > -   rq = task_rq_lock(p, &flags);
> >> > -   dest_cpu = p->sched_class->select_task_rq(rq, p, SD_BALANCE_EXEC, 0);
> >> > +   raw_spin_lock_irqsave(&p->pi_lock, flags);
> >>
> >> Seems this should go to patch 07/17 ;)
> >
> > Ah, the reason its here is that this patch removes the rq argument and
> > thus we no longer need rq->lock. So this part relies on the property
> > introduced by patch 7.
> 
> What I mean is we could firstly add pi_lock in patch 7 and then remove
> the rq argument in this patch. :)

No, that's the wrong way around.. anyway, I've pulled this into its own
patch and the next posting should hopefully be clearer.
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