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Subject: Re: [PATCH 4/4] sched: add hooks for workqueue
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: mingo@elte.hu, linux-kernel@vger.kernel.org,
       Mike Galbraith <efault@gmx.de>
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Date: Mon, 31 May 2010 10:01:07 +0200
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On Thu, 2010-05-13 at 12:48 +0200, Tejun Heo wrote:
> Concurrency managed workqueue needs to know when workers are going to
> sleep and waking up, and, when a worker goes to sleep, be able to wake
> up another worker to maintain adequate concurrency.  This patch
> introduces PF_WQ_WORKER to identify workqueue workers and adds the
> following two hooks.
> 
> * wq_worker_waking_up(): called when a worker is woken up.
> 
> * wq_worker_sleeping(): called when a worker is going to sleep and may
>   return a pointer to a local task which should be woken up.  The
>   returned task is woken up using try_to_wake_up_local() which is
>   simplified ttwu which is called under rq lock and can only wake up
>   local tasks.

This changelog seems to lack explanation for why you need the wakeup
callback.