linux-kernel - Re: [PATCHSET] workqueue: reimplement CPU hotplug to keep idle workers

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Date:	Fri, 20 Jul 2012 19:01:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, linux-pm@...r.kernel.org
Subject: Re: [PATCHSET] workqueue: reimplement CPU hotplug to keep idle
 workers

On Fri, 2012-07-20 at 09:52 -0700, Tejun Heo wrote:
> Ooh, yeah, I agree.  That's next on the wq to-do list.  The problem is
> that queue_work() is implemented in terms of queue_work_on().  

But that's trivial to fix, both could use __queue_work() without too
much bother, right?

> In most
> cases, the local binding serves as locality optimization than anything
> else.  There are use cases where affinity is required for correctness.

> The assumption was that they should flush during CPU_DOWN but it
> probably will be much better to require users which need CPU affinity
> to always use queue_work_on() - instead of implicit local affinity
> from queue_work() - and flush them automatically from wq callback.
> 

Right, and when you create this new mode, which you need to know to
flush on DOWN, you can simply put a BUG_ON in queue_work_on() when this
mode is set.


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