linux-kernel - Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed for kthreadd V2

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Message-ID: <0000014238407a1c-34e7bdbc-45c0-48de-a8a3-94a99f276044-000000@email.amazonses.com>
Date:	Fri, 8 Nov 2013 15:06:59 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Frysinger <vapier@...too.org>
Subject: Re: [PATCH] kmod: Run usermodehelpers only on cpus allowed for
 kthreadd V2

On Thu, 7 Nov 2013, Frederic Weisbecker wrote:

> usermodehelper works are created via workqueues, right? And workqueues are an issue as
> well for those who want CPU isolation.

AFAICT usermodehelper can be called from a variety of contexts.

> So this looks like a more general problem than just call_usermodehelper.

Well the code explicitly sets the the affinity mask to all cpus which
creates a problem for low latency processors. It does not inherit the
affinity from any calling process.

> Last time I checked, it seemed to me that this is an unbound workqueue? If so can't we tune
> the affinity of this workqueue? If not perhaps that's something we want to solve and which
> could be useful for all the users who don't want their CPU to be disturbed.

There are various contexts from which usermodehelper can be called.
Drivers use it etc.
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