Re: [PATCHSET] workqueue: reimplement CPU hotplug to keep idleworkers

From: Peter Zijlstra
Date: Fri Jul 20 2012 - 13:02:03 EST

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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