linux-kernel - Re: [RFC 0/12][PATCH] SCHED_DEADLINE: fork and terminate task logic

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Date:	Wed, 13 Jan 2010 12:11:07 +0100
From:	Raistlin <raistlin@...ux.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	michael trimarchi <michael@...dence.eu.com>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	Chris Friesen <cfriesen@...tel.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Henrik Austad <henrik@...tad.us>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Sven-Thorsten Dietrich <sven@...bigcorporation.com>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
	"giuseppe.lipari" <giuseppe.lipari@...up.it>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [RFC 0/12][PATCH] SCHED_DEADLINE: fork and terminate task logic

On Tue, 2009-12-29 at 16:20 +0100, Peter Zijlstra wrote:
> > -       if (!rt_prio(p->prio))
> > +               /*
> > +                * the child will be SCHED_DEADLINE, but with zero bandwidth.
> > +                * The parent (or some other task) must call setscheduler_ex
> > +                * on it, or it won't ever start.
> > +                */
> > +               init_deadline_task(p);
> > +               p->dl.flags &= ~DL_NEW;
> > +               p->dl.flags |= DL_THROTTLED;
> 
> I recently added ->task_fork(), which is called after the class
> assignment.
> 
Saw that, and it is being of great help! :-P

> > +       } else if (rt_prio(p->prio))
> > +               p->sched_class = &rt_sched_class;
> > +       else
> >                 p->sched_class = &fair_sched_class;
> >  
> >  #ifdef CONFIG_SMP
> > @@ -2744,6 +2756,10 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
> >         if (mm)
> >                 mmdrop(mm);
> >         if (unlikely(prev_state == TASK_DEAD)) {
> > +               /* a deadline task is dying: stop the bandwidth timer */
> > +               if (deadline_task(prev))
> > +                       hrtimer_cancel(&prev->dl.dl_timer);
> > +
> >                 /*
> >                  * Remove function-return probe instances associated with this
> >                  * task and put them back on the free list. 
> 
> Shouldn't this be done in the ->dequeue_task() callback?
>
Not sure of this snippet... Actually, it is one of the most disturbing
piece of code of this whole scheduler. :-(

The reason why it is here is that I think it is needed to call
hrtimer_cancel() _without_ holding the rq->lock, is that correct?

It is 

Thanks and regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://blog.linux.it/raistlin / raistlin@...ga.net /
dario.faggioli@...ber.org

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