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

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Date:	Wed, 11 Jan 2012 18:29:15 +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 Wed, 2012-01-11 at 23:22 +0600, Rakib Mullick wrote:
> Hello all,
> 
> In ttwu_do_activate(), we're decrementing nr_uninterruptible if
> p->sched_contributes_to_load (for SMP=y). But, we're also decrementing
> nr_uninterruptible from activate_task at the same path. Why we're
> doing it twice for a single task activation path?

activate_task() does:

 if (task_contributes_to_load(p))
   rq->nr_uninterruptible--;

Now task_contributes_to_load() reads like:

#define task_contributes_to_load(task)	\
				((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
				 (task->flags & PF_FREEZING) == 0)

which will be false, since we've set TASK_WAKING.
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