linux-kernel - Re: [PATCH 2/5] kmod: Use system_unbound

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Date:	Fri, 10 Jul 2015 20:10:57 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/5] kmod: Use system_unbound_wq instead of khelper

On Fri, Jul 10, 2015 at 12:52:39PM -0500, Christoph Lameter wrote:
> On Fri, 10 Jul 2015, Frederic Weisbecker wrote:
> 
> > No it's not much configurable. The works are scheduled on tasks that are
> > node affine and you can't change that for system_unbound_wq. Only WQ_SYSFS
> > workqueues can be overriden on their no_numa property but even there that's
> > after the boot and most of the usermodehelper load goes on boot.
> 
> Well then lets have at least one thread per NUMA node so that NUMA
> affinity works?

That's already the case. There is at least one thread per node for the
workqueue cpumask.

Note that nohz full is perfectly fine with that. The issue I'm worried about
is the case where drivers spawn hundreds of jobs and it all happen on the same
node because the kernel threads inherit the workqueue affinity, instead of
the global affinity that khelper had.

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