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

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Date:	Thu, 17 Oct 2013 15:24:36 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	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>,
	Andrew Morton <akpm@...ux-foundation.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

On Thu, 17 Oct 2013, Frederic Weisbecker wrote:

> > -	/* We can run anywhere, unlike our parent keventd(). */
> > -	set_cpus_allowed_ptr(current, cpu_all_mask);
> > +	/* We can run anywhere kthreadd can run */
> > +	set_kthreadd_affinity();
>
> If you really want your isolated CPUs to be undisturbed, you need this affinity to
> be set before the creation of this usermode helper. Otherwise it's going to run to any random
> place before you call the above function.
>
> Is there now way to control the kworker affinity which create this usermode helpers threads
> instead?

The invocation is coming from keventd so the affinity seems to be set to
a different cpu before we get the thread moved.

A tsc loop is running on the processor that gets hit by the usermodehelper spawns.

We see spawning by the tty notifier (when typing on a vt) as well as by a
mellanox driver (periodically).

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