linux-kernel - Re: [Question] sched: Should nr_uninterruptible be decremented in ttwu_do

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Date:	Thu, 12 Jan 2012 21:25:45 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Question] sched: Should nr_uninterruptible be decremented in
 ttwu_do_activate()?

On Thu, 2012-01-12 at 23:08 +0600, Rakib Mullick wrote:

> That might be the case for scheduler_ipi(), but when
> sched_ttwu_pending() gets called when a cpu goes down, all tasks from
> wake_list of that cpu has been moved without TASK_WAKING is set. For a
> particular task it might be possible that when it ran previously it
> had p->sched_contributes_to_load is set. Latter, this task's cpu has
> been put down and calls sched_ttwu_pending(), then for that task
> p->sched_contributes_to_load is set and TASK_WAKING is not set.
> Couldn't be happen?

No, look again, its impossible to be on that list and not be
TASK_WAKING.

The only way onto the list is through ttwu_queue_remote(), the only way
off the list is through sched_ttwu_pending(). 
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