linux-kernel - Re: [PATCH] workqueue: Restore cpus_allowed mask for sleeping workqueue rescue threads

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Message-ID: <20110930080914.GM10425@mtj.dyndns.org>
Date:	Fri, 30 Sep 2011 01:09:14 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	Ripduman Sohan <Ripduman.Sohan@...cam.ac.uk>,
	linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: Re: [PATCH] workqueue: Restore cpus_allowed mask for sleeping
 workqueue rescue threads

Hello,

On Sun, Sep 25, 2011 at 09:02:25AM +0300, Gilad Ben-Yossef wrote:
> Thank you for taking the time to answer my query :-)
> 
> I agree there is no real problem with having an additional task
> bound to an "isolated" CPU so long that it does not run and of
> course that if a task on an isolated CPU initiated activity that
> resulted in requiring the services of a rescuer workqueue thread it
> most certainly needs to run there and that is fine.
> 
> I guess my question is - apart form running on the isolated CPU,
> does the fact that the rescuer thread is bound there can cause
> activity on that CPU originating from a foreign CPU, such as for
> example running an IPI handler in order to migrate it there?

Hmmm... indeed.  This can cause an unnecessary wakeup / migration on
an isolated CPU when another CPU asks for the rescuer, so yeah it
makes sense to change the behavior.  BTW, why didn't the original
patch simply use set_cpus_allowed_ptr(cpu_all_mask)?

Thanks.

-- 
tejun
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