linux-kernel - Re: [PATCH RFC] reduce runqueue lock contention

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Message-ID: <1291275409.4023.21.camel@twins>
Date:	Thu, 02 Dec 2010 08:36:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	frank.rowand@...sony.com
Cc:	Chris Mason <chris.mason@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	"axboe@...nel.dk" <axboe@...nel.dk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, tglx <tglx@...utronix.de>
Subject: Re: [PATCH RFC] reduce runqueue lock contention

On Wed, 2010-12-01 at 15:13 -0800, Frank Rowand wrote:
> 
>   If the task to be woken is on a run queue on a different cpu then use
>   cmpxchg() to put it onto a pending try_to_wake_up list on the different
>   cpu.  Then send an interrupt to the different cpu to cause that cpu to
>   call try_to_wake_up() for each process on the try_to_wake_up list. 

Without having looked at the actual code, the described thing cannot
work, try_to_wake_up() has a return value that needs to be passed back.

Also, try_to_wake_up() does load-balancing, you really want to do that
before queueing it on a remote cpu.
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