linux-kernel - Re: [patch] Re: autogroup: sched

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Message-ID: <1294771686.8006.15.camel@marge.simson.net>
Date:	Tue, 11 Jan 2011 19:48:06 +0100
From:	Mike Galbraith <efault@....de>
To:	bharata@...ux.vnet.ibm.com
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [patch] Re: autogroup: sched_setscheduler() fails

On Tue, 2011-01-11 at 22:40 +0530, Bharata B Rao wrote:
> On Mon, Jan 10, 2011 at 05:42:26PM +0100, Mike Galbraith wrote:
> > Index: linux-2.6/kernel/sched_autogroup.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched_autogroup.c
> > +++ linux-2.6/kernel/sched_autogroup.c
> > @@ -73,6 +73,15 @@ static inline struct autogroup *autogrou
> >  	ag->id = atomic_inc_return(&autogroup_seq_nr);
> >  	ag->tg = tg;
> >  	tg->autogroup = ag;
> > +#ifdef CONFIG_RT_GROUP_SCHED
> > +	/*
> > +	 * HACK: autogroup RT tasks run in the root task group.
> > +	 * This fools __sched_setscheduler() into proceeding on
> > +	 * so we can move the task to the appropriate runqueue
> > +	 * upon scheduling policy change.
> > +	 */
> > +	tg->rt_bandwidth.rt_runtime = RUNTIME_INF;
> > +#endif
> > 
> >  	return ag;
> > 
> > @@ -143,6 +152,15 @@ autogroup_move_group(struct task_struct
> >  	autogroup_kref_put(prev);
> >  }
> > 
> > +static inline void
> > +autogroup_setscheduler(struct task_struct *p, int on_rq)
> > +{
> > +	if (p->sched_class->task_move_group)
> > +		p->sched_class->task_move_group(p, on_rq);
> > +	else
> > +		set_task_rq(p, task_cpu(p));
> > +}
> > +
> 
> IIUC, with the above changes you are actually queing the task into
> rt_rq of an autogroup. But the task's autogroup interface
> (/proc/<pid>/autogroup) allows you to control the bandwidth of only
> cfs_rq tasks, while the rt tasks in the group get RUNTIME_INF bandwidth.
> 
> I think what we need is a real group change here (which is difficult I
> think) and not just sched_class change.

Unless I fscked up, set_task_rq() is the group change.  As soon as the
task's class changes, it'll be moved to the root_task_group.

	-Mike

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