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

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Message-ID: <20150331210636.GJ9974@htj.duckdns.org>
Date:	Tue, 31 Mar 2015 17:06:36 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	cmetcalf@...hip.com,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"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 Tue, Mar 31, 2015 at 10:58:41PM +0200, Frederic Weisbecker wrote:
> On Tue, Mar 31, 2015 at 03:25:59PM -0400, cmetcalf@...hip.com wrote:
> > From: Chris Metcalf <cmetcalf@...hip.com>
> > 
> > When queuing work, we should avoid queuing it on the local cpu if
> > we are using WORK_CPU_UNBOUND and the local cpu is nohz_full, since
> > the workqueue will mean a later interrupt of the nohz_full process
> > that presumably would prefer continuing to have 100% of the core
> > without interrupts.
> > 
> > Likewise, remove the nohz_full cores from unbound workqueues.  If
> > all the cores are nohz_full, we leave them in.
> > 
> > Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> 
> Lai is already working on this: https://lkml.org/lkml/2015/3/12/27
> 
> All that will be needed after this patchset is to force the desired
> unbound workqueue mask on boot.

This applies to per-cpu workqueues too, not just unbound workqueues.

Thanks.

-- 
tejun
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