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

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Date:	Tue, 29 Dec 2009 16:20:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raistlin <raistlin@...ux.it>
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>,
	Bjoern Brandenburg <bbb@...unc.edu>,
	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 Fri, 2009-10-16 at 17:41 +0200, Raistlin wrote:
> +++ b/kernel/sched.c
> @@ -2561,8 +2561,20 @@ void sched_fork(struct task_struct *p, int clone_flags)
>          * Make sure we do not leak PI boosting priority to the child.
>          */
>         p->prio = current->normal_prio;
> +       if (deadline_task(p)) {
> +               p->sched_class = &deadline_sched_class;
>  
> -       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.

> +       } 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?

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