linux-kernel - Re: [PATCH 4/4] sched: add hooks for workqueue

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Message-ID: <4C038841.1010507@kernel.org>
Date:	Mon, 31 May 2010 11:58:25 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 4/4] sched: add hooks for workqueue

Hello, Peter.

On 05/31/2010 10:01 AM, Peter Zijlstra wrote:
> 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.

Because cmwq "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".  Sure, I can add more but
again forward reference here would work pretty well when digging
through history.

-- 
tejun
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