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Subject: Re: [RFC/RFT PATCH] sched: automated per tty task groups
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <efault@gmx.de>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@linux-foundation.org>
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Date: Tue, 19 Oct 2010 11:29:52 +0200
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On Tue, 2010-10-19 at 11:16 +0200, Mike Galbraith wrote:
> +       read_lock_irqsave(&tasklist_lock, flags);
> +
> +       rcu_read_lock();
> +       for_each_process(p) {
> +               tg = task_group(p);
> +               tty_sched_move_task(p, tg);
> +               list_for_each_entry_rcu(t, &p->thread_group, thread_group) {
> +                       tty_sched_move_task(t, tg);
> +               }
> +       }
> +       rcu_read_unlock();
> +
> +       read_unlock_irqrestore(&tasklist_lock, flags); 

I don't think you need to disable IRQs for tasklist lock, nor do I think
you actually need it.

If you enable tty groups and then scan all the existing tasks you've
covered them all, new tasks will already be placed right, dying tasks we
don't care about anyway.