linux-kernel - Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task when changing task groups

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Message-ID: <20160606191552.GE8105@intel.com>
Date:	Tue, 7 Jun 2016 03:15:52 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, bsegall@...gle.com, pjt@...gle.com,
	morten.rasmussen@....com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com
Subject: Re: [PATCH v4 3/5] sched/fair: Skip detach sched avgs for new task
 when changing task groups

On Mon, Jun 06, 2016 at 03:03:38PM +0100, Matt Fleming wrote:
> >  #ifdef CONFIG_FAIR_GROUP_SCHED
> > -static void task_move_group_fair(struct task_struct *p)
> > +static void task_move_group_fair(struct task_struct *p, bool fork)
> >  {
> > -	detach_task_cfs_rq(p);
> > +	/*
> > +	 * Newly forked task should not be removed from any cfs_rq
> > +	 */
> > +	if (!fork)
> > +		detach_task_cfs_rq(p);
> >  	set_task_rq(p, task_cpu(p));
> >  	attach_task_cfs_rq(p);
> >  	/*
> 
> Wouldn't it be more symmetric to add,
> 
> 	if (p->se.avg.last_update_time)
> 		__update_load_avg(...)
> 
> to detach_entity_load_avg() so that there's no need to pass the @fork
> parameter all the way down the stack

Up to this point, we can't. But we should be able to if we move the next
patch (4/5) before this patch. I should have changed my mindset with that
patch. Good advice though, thanks, Matt.