linux-kernel - Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

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Message-ID: <20090126224252.GA30160@elte.hu>
Date:	Mon, 26 Jan 2009 23:42:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, a.p.zijlstra@...llo.nl,
	rusty@...tcorp.com.au, travis@....com, mingo@...hat.com,
	davej@...hat.com, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.


* Oleg Nesterov <oleg@...hat.com> wrote:

> On 01/26, Ingo Molnar wrote:
> >
> > Andrew's suggestion does make sense though: for any not-in-progress
> > worklet we can dequeue that worklet and execute it in the flushing
> > context. [ And if that worklet cannot be dequeued because it's being
> > processed then that's fine and we can wait on that single worklet, without
> > waiting on any other 'unrelated' worklets. ]
> 
> Yes sure. This is easy, and I am not sure we need the special handler.
> If the caller wants this behaviour, it can do:
> 
> 	if (cancel_work_sync(work))
> 		work->func(work);
> 
> But flush_work() was specially introduced for the case when we can't
> do the above,

it would be better to have this implicit in some wait_for_work() facility 
(which flush_work() really is) - because it is not intuitive to code a 
serialization as a 'cancel + execute open-coded' sequence.

> > That does not help work_on_cpu() though: that facility really uses the 
> > fact that workqueues are implemented via per CPU threads - hence we 
> > cannot remove the worklet from the queue and execute it in the 
> > flushing context.
> 
> Yes.

it's arguably a (mild, albeit elegant) abuse of workqueue internals 
though.

	Ingo
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