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

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Date:	Fri, 30 Sep 2011 09:54:21 +0100
From:	Ripduman Sohan <Ripduman.Sohan@...cam.ac.uk>
To:	Tejun Heo <tj@...nel.org>
Cc:	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: Re: [PATCH] workqueue: Restore cpus_allowed mask for sleeping
 workqueue rescue threads

Tejun Heo <tj@...nel.org> wrote:

> 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)?
> 

Because while at present all (bound) rescuer threads have an associated workqueue on each CPU, I didn't want to assume this arrangement would _always_ be the case.  It was my thinking that for bound threads, iterating over the CPUs to only set those that have an associated workqueue for the rescuer would insulate agsinst any future case where rescuer threads may be bound to a subset of CPUs.

Kind regards,

--rip

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