linux-kernel - Re: [GIT PULL] workqueue fixes for v4.3-rc5

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Message-ID: <alpine.DEB.2.20.1510141356360.13663@east.gentwo.org>
Date:	Wed, 14 Oct 2015 13:58:30 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Shaohua Li <shli@...com>, linux-mm <linux-mm@...ck.org>
Subject: Re: [GIT PULL] workqueue fixes for v4.3-rc5

On Wed, 14 Oct 2015, Linus Torvalds wrote:

> On Wed, Oct 14, 2015 at 10:57 AM, Christoph Lameter <cl@...ux.com> wrote:
> >
> > Well yes the schedule_delayed_work_on() call is from another cpu and the
> > schedule_delayed_work() from the same. No confusion there.
>
> So "schedule_delayed_work()" does *not* guarantee that the work will
> run on the same CPU.

That is news to me. As far as I know: The only workqueue that is not
guaranteed to run on the same cpu is an unbound workqueue.

> If you want the scheduled work to happen on a particular CPU, then you
> should use "schedule_delayed_work_on()"  It shouldn't matter which CPU
> you call it from.

Ok then lets audit the kernel for this if that assumption is no longer
true.

> At least that's how I think the rules should be. Very simple, very
> clear: if you require a specific CPU, say so. Don't silently depend on
> "in practice, lots of times we tend to use the local cpu".

As far as I can remember this was guaranteed and not just practice.

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