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Date: Thu, 11 Nov 2010 17:32:43 +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>,
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Subject: Re: [RFC][PATCH 06/22] sched: SCHED_DEADLINE handles spacial
	kthreads
Message-ID: <20101111163242.GA5697@redhat.com>
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On 11/11, Peter Zijlstra wrote:
>
> On Thu, 2010-11-11 at 16:27 +0100, Oleg Nesterov wrote:
> >
> > 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?
>
> Yes, I think we can make that work, we could even move that
> migrate_live_tasks() into CPU_DYING, which is before this point.

Hmm, I think you are right. In this case we can also simplify
migrate-from-dead-cpu paths, we know that nobody can touch rq->lock,
every CPU runs stop_machine_cpu_stop() with irqs disabled. No need
to get/put task_struct, etc.

Oleg.