linux-kernel - Re: [RFC v2][PATCH] create workqueue threads only when needed

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Date:	Thu, 29 Jan 2009 05:58:48 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alasdair G Kergon <agk@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC v2][PATCH] create workqueue threads only when needed

On 01/29, Frederic Weisbecker wrote:
>
> I was about to retry the same approach but through async functions (kernel/async.c)
> which would have solved the possible deadlock you described and would have made
> the synchronizations easier.
>
> But actually this is only a half solution:
>
> Pointless workqueues stay pointless, even if they don't appear before they run once.
> And moreover this is hiding the real problem: parts of the kernel use dedicated workqueues
> while kevent is sufficient most of the time.
>
> And if there are problems with using the workqueues, because of deadlocks or slow
> works, async functions are a good solution.

Completely agreed.

And. Even if some subsystem really needs its own workqueue, probably it
can use the single-threaded one, but we have a lot of multithreaded wqs.

Oleg.

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