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Message-ID: <4986B684.5000506@s5r6.in-berlin.de>
Date: Mon, 02 Feb 2009 10:01:56 +0100
From: Stefan Richter <stefanr@s5r6.in-berlin.de>
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To: Arjan van de Ven <arjan@infradead.org>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Lai Jiangshan <laijs@cn.fujitsu.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC][PATCH] create workqueue threads only when needed
References: <20090127001708.GA4815@nowhere>	<20090126163015.7f879b18@infradead.org>	<20090131180347.GC5884@nowhere>	<20090131101502.7ce8e7af@infradead.org>	<20090131182843.GD5884@nowhere>	<1233524261.18767.60.camel@pasglop> <20090201211909.37c0780b@infradead.org>
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Arjan van de Ven wrote:
> On Mon, 02 Feb 2009 08:37:41 +1100
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
>> That's were thread pools kick in ... tried using Dave Howells slow
>> work ?
> 
> async function calls are pretty much the same and actually in mainlinme.
> Dave Howells stuff in addition plays some extremely weird refcounting
> games that I cannot imagine anyone but him needing...

I haven't looked at this particular slow-work implementation.  Do you
refer to some internal refcounting or to some refcounting as a service
for the API user?

IME, scheduling work and executing work is often accompanied by
reference counting of this sort:

static int schedule_delayed_work_wrapper(struct foo *container,
					 unsigned long delay)
{
	int scheduled;

	foo_get(container);
	scheduled = schedule_delayed_work(&container->work, delay);
	if (!scheduled)
		foo_put(container);

	return scheduled;
}

static void foo_work(struct work_struct *work)
{
	struct foo *container =
			container_of(work, struct foo, work.work);

	do_the_work;

	foo_put(container);
}

But I think that whenever there are additional call sites of
foo_put(container), this refcounting of container_of(work, ...) cannot
be easily generalized.
-- 
Stefan Richter
-=====-==--= --=- ---=-
http://arcgraph.de/sr/