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Date: Thu, 11 Nov 2010 16:27:51 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Raistlin <raistlin@linux.it>, Ingo Molnar <mingo@elte.hu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Fabio Checconi <fabio@gandalf.sssup.it>,
        Tommaso Cucinotta <cucinotta@sssup.it>,
        Juri Lelli <juri.lelli@gmail.com>,
        Nicola Manica <nicola.manica@disi.unitn.it>,
        Luca Abeni <luca.abeni@unitn.it>, Dhaval Giani <dhaval@retis.sssup.it>,
        Harald Gustafsson <hgu1972@gmail.com>,
        paulmck <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 06/22] sched: SCHED_DEADLINE handles spacial
	kthreads
Message-ID: <20101111152750.GA2510@redhat.com>
References: <1288333128.8661.137.camel@Palantir> <1288333876.8661.147.camel@Palantir> <1289486096.2084.123.camel@laptop>
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On 11/11, Peter Zijlstra wrote:
>
> On Fri, 2010-10-29 at 08:31 +0200, Raistlin wrote:
> > @@ -6071,7 +6104,7 @@ void sched_idle_next(void)
> >          */
> >         raw_spin_lock_irqsave(&rq->lock, flags);
> >
> > -       __setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
> > +       __setscheduler_dl_special(rq, p);
> >
> >         activate_task(rq, p, 0);
> >
>
> Ingo, happen to know if this is really needed these days? hotplug should
> have migrated all other tasks away, leaving only the idle task to run.

This is called before CPU_DEAD stage which migrates all tasks away.


Sorry, can't resist, off-topic quiestion. Do we really need
migration_call()->migrate_live_tasks() ?

With the recent changes, try_to_wake_up() can never choose
the dead (!cpu_online) cpu if the task was deactivated.

Looks like we should only worry about the running tasks, and
migrate_dead_tasks()->pick_next_task() loop seems to all work
we need.

(Of course, we can't just remove migrate_live_tasks(), at leat
 migrate_dead() needs simple changes).

What do you think?

Oleg.