linux-kernel - Re: [RFC] workqueue: avoiding unbounded wq on isolated CPUs by default

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Message-ID: <20150717153507.GB20260@lerouge>
Date:	Fri, 17 Jul 2015 17:35:09 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Rik van Riel <riel@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>
Subject: Re: [RFC] workqueue: avoiding unbounded wq on isolated CPUs by
 default

On Fri, Jul 17, 2015 at 11:27:20AM -0400, Tejun Heo wrote:
> Hello, Mike.
> 
> On Fri, Jul 17, 2015 at 06:26:30AM +0200, Mike Galbraith wrote:
> > Hm, I thought the plan was that after the Lai's unbound series landed,
> > his ordered wq patch would follow, but perhaps not.
> 
> Yes, that still is the plan but this is kinda unrelated to that
> change.  This just initializes wq cpumask according to cpu isolation.
> I'm just curious whether there was any specific reason we didn't do
> this before (ISTR people discussing it back then too).

Initializing wq unbound cpumask to housekeeping_mask is still the
plan. I just remember we didn't do it in Lai's series because it
was slightly unrelated. When a patchset is complicated, like Lai's,
it's better to keep it focus to a single purpose.

Anyway that patch is welcome.

> 
> > I'm referring to the somewhat aged patch below. (freshly wedged into
> > master, and maybe not properly, but it should at least look familiar).
> 
> Yeah, I think I asked Lai to try a different approach where we
> regulate it from queueing path rather than playing with pwqs.  I think
> that'd end up quite a bit simpler.

Ordered workqueues aren't handled currently? I tried setting the unbound
cpumask and it also applied to khelper which is a singlethread (and thus
ordered) workqueue.

> Thanks.
> 
> -- 
> tejun
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