linux-kernel - Re: [PATCH 04/10] nohz: Remove useless argument on tick_nohz_task

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Message-ID: <20150803130450.GN25159@twins.programming.kicks-ass.net>
Date:	Mon, 3 Aug 2015 15:04:50 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 04/10] nohz: Remove useless argument on
 tick_nohz_task_switch()

On Mon, Aug 03, 2015 at 02:49:54PM +0200, Frederic Weisbecker wrote:
> On Mon, Aug 03, 2015 at 02:39:59PM +0200, Peter Zijlstra wrote:
> > On Thu, Jul 23, 2015 at 06:42:09PM +0200, Frederic Weisbecker wrote:
> > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > index 78b4bad10..4d34035 100644
> > > --- a/kernel/sched/core.c
> > > +++ b/kernel/sched/core.c
> > > @@ -2489,7 +2489,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> > >  		put_task_struct(prev);
> > >  	}
> > >  
> > > -	tick_nohz_task_switch(current);
> > > +	tick_nohz_task_switch();
> > >  	return rq;
> > >  }
> > 
> > OK, so I just noticed this one. Please explain? WTF does it make sense
> > to have per task tick state?
> > 
> > If we have >1 tasks, we need the tick. If we have 1 task, per-task ==
> > per-cpu.
> > 
> > So what gives?
> 
> tick_nohz_task_switch() is removed in the end of the patchset. There is no
> more per task dependency after this specific set.

OK, I'll keep reading ;-)
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