linux-kernel - Re: [PATCH 17/21] workqueue: simple reimplementation of SINGLE

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Date:	Tue, 17 Nov 2009 15:03:17 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, jeff@...zik.org, mingo@...e.hu,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com,
	torvalds@...ux-foundation.org, avi@...hat.com,
	peterz@...radead.org, andi@...stfloor.org, fweisbec@...il.com
Subject: Re: [PATCH 17/21] workqueue: simple reimplementation of
 SINGLE_THREAD workqueue

On Tue, 2009-11-17 at 02:15 +0900, Tejun Heo wrote:
> SINGLE_THREAD workqueues are used to reduce the number of worker
> threads and ease synchronization.

Wireless (mac80211) also requires that the order in which different work
structs are queued up is identical to the processing order. At least
some code was written with that assumption in mind, and I think it's
actually required in a few places.

Also, that unlikely() here:

> +	if (unlikely(single_thread)) {
> +		mutex_lock(&wq->single_thread_mutex);
> +		f(work);
> +		mutex_unlock(&wq->single_thread_mutex);
> +	} else
> +		f(work);

seems wrong, there are many single-threaded workqueues after all.

johannes

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