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

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Message-ID: <20110930085714.GB23868@mtj.dyndns.org>
Date:	Fri, 30 Sep 2011 01:57:14 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Ripduman Sohan <Ripduman.Sohan@...cam.ac.uk>
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

On Fri, Sep 30, 2011 at 09:54:21AM +0100, Ripduman Sohan wrote:
> 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.

On which CPU a rescuer is doesn't matter at all.  Using cpu_all_mask
is good enough.

Thank you.

-- 
tejun
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