linux-kernel - Re: [PATCH 3/3 V8] workqueue: Allow modifying low level unbound workqueue cpumask

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Date:	Tue, 28 Apr 2015 06:36:44 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	Christoph Lameter <cl@...ux.com>,
	Kevin Hilman <khilman@...aro.org>,
	Mike Galbraith <bitbucket@...ine.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 3/3 V8] workqueue: Allow modifying low level unbound
 workqueue cpumask

On Mon, 2015-04-27 at 23:44 -0400, Tejun Heo wrote:

> > So, we need an API to modify the wq_unbound_cpumask, and I provided
> > this public function.  Otherwise, the other code can't modify it.
> 
> I see.  I don't have too strong an opinion; however, changing the mask
> is a fairly heavy operation.  Are there specific reasons why we don't
> want to follow the nohz config right away?

Isolation is not only applicable to nohz_full.  Many loads are
unsuitable for nohz_full, yet require maximum isolation.

ATM, nohz_full is not dynamic, but hopefully one day will be.  In the
here and now, we can isolate cores from the scheduler on the fly via
cpusets, a prime API user candidate.

	-Mike

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