linux-kernel - Re: [patch] workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound

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Date:	Wed, 22 Jul 2015 17:19:00 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lai Jiangshan <jiangshanlai@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Subject: Re: [patch] workqueue: schedule WORK_CPU_UNBOUND work on
 wq_unbound_cpumask CPUs

On Wed, 2015-07-22 at 16:55 +0200, Mike Galbraith wrote:
> On Wed, 2015-07-22 at 10:11 -0400, Tejun Heo wrote:
> > On Wed, Jul 22, 2015 at 07:24:46AM +0200, Mike Galbraith wrote:
> > > WORK_CPU_UNBOUND work items queued to a bound workqueue always run
> > > locally.  This is a good thing normally, but not when the user has
> > 
> > The constant name used there is a bit misleading but you can't put
> > work items which are queued w/ queue_work() on foreign cpus by
> > default.  queue_work() has always guaranteed local execution.  The
> > problem is that workqueue can't currently tell whether a queue_work()
> > user expects cpu locality for correctness or optimization.  It'd be
> > great if we introduce queue_work_on_local() or sth and replace
> > correctness ones with it but that involves auditing each and every
> > queue_work() usage.  If anybody is up for the task, I'd be happy to
> > help.
> 
> Oh well.  That puts a big dent in the utility of wq_unbound_cpumask, but
> too bad.  If someone has a big enough HPC itch, they'll scratch it.

Ew, looking at the numbers, they may prefer to either a) pretend to not
notice, or b) scurry off to HPC'R'US store if a) won't fly ;-)

	-Mike

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