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Date:	Thu, 3 Apr 2014 17:05:24 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	LKML <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>
Subject: Re: [PATCH 3/4] workqueue: Add anon workqueue sysfs hierarchy

On Thu, Apr 03, 2014 at 10:58:05AM -0400, Tejun Heo wrote:
> Hello, Frederic.
> 
> On Thu, Apr 03, 2014 at 04:42:55PM +0200, Frederic Weisbecker wrote:
> > > I'm not really sure this is the good approach.  I think I wrote this
> > > way back but wouldn't it make more sense to allow userland to restrict
> > > the cpus which are allowed to all unbound cpus.  As currently
> > > implemented, setting WQ_SYSFS to give userland more control would
> > > escape that workqueue from this global mask as a side effect, which is
> > > a surprising behavior and doesn't make much sense to me.
> > 
> > I just considered that anon workqueues shouldn't be that different from
> > another WQ_SYSFS workqueue. This way we don't have suprising side effect.
> > Touching a WQ_SYSFS doesn't impact anon workqueues, and touching anon workqueues
> > doesn't impact WQ_SYSFS workqueues.
> 
> I really think it'd be a lot better to perceive the default attributes
> to be layered below explicit WQ_SYSFS attributes; otherwise, we have
> two disjoint sets and the workqueues would jump between the two
> depending on WQ_SYSFS.  A system tool which wants to configure all
> workqueues would have to scan and manipulate all of them not knowing
> what specific one's requirements are and tools which want to configure
> specific ones likely won't know what the overruling condition is and
> violate the global contraints.  It'd be clearer to have the layering
> pre-defined and enforced.

Ok, works for me.

> 
> > In fact this is simply the current way we do it, just extended.
> 
> Yes, in term of mechanics, it is but I don't think that's what we
> want.  We want to be able to say "unbound workqueues in general are
> confined to these cpus" and it's weird to just provide knobs for wqs
> which don't have knobs.

Yeah I like the simplicity of that.

> 
> > Yeah I like this. So the right place for this cpumask would be in
> > the root of /sys/devices/virtual/workqueue/ , right?
> 
> Yes, I think that'd make more sense.

Ok, I'll try this. Thanks!

> 
> Thanks.
> 
> -- 
> tejun
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