linux-kernel - Re: [PATCH] workqueue: avoid nohz

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Message-ID: <20150401154637.GN9974@htj.duckdns.org>
Date:	Wed, 1 Apr 2015 11:46:37 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	cmetcalf@...hip.com, Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: avoid nohz_full cores

On Wed, Apr 01, 2015 at 09:56:07AM +0200, Peter Zijlstra wrote:
> > The problem with this is that workqueue currently doesn't distinguish
> > why work items are queued on per-cpu workqueues.  It can't tell
> > whether being bound to local CPU is for correctness or optimization
> > and thus can't break local execution guarantee for anybody.  We need
> > to hunt down all the ones which depend on local execution and annotate
> > them with explicit queue_work_on() before being able to do this.
> 
> This is moot on unbound workqueues, they can run wherever so it can
> never be a correctness thing, right?

The posted patch applies to both unbound and per-cpu workqueues.
There's a more comprehensive patchset currently being worked on by Lai
for unbound workqueues.

Thanks.

-- 
tejun
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