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Subject: Re: [PATCH RFC] reduce runqueue lock contention
From: Peter Zijlstra <peterz@infradead.org>
To: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>, axboe@kernel.dk, linux-kernel@vger.kernel.org
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	 <1274389786.1674.1653.camel@laptop>
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Date: Thu, 20 May 2010 23:23:12 +0200
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On Thu, 2010-05-20 at 23:09 +0200, Peter Zijlstra wrote:

> int try_to_wake_up(struct task *p, unsigned int mask, wake_flags)
> {
>   int state = atomic_read(&p->state);
> 
>   do {
>     if (!(state & mask))
>       return 0;
> 
>     state = atomic_cmpxchg(&p->state, state, TASK_WAKING);
>   } while (state != TASK_WAKING);

    cpu = select_task_rq()

and then somehow see we get set_task_cpu() done without races :-)

>   /* do this pending queue + ipi thing */
> 
>   return 1;
> }