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Date: Mon, 23 Sep 2013 15:10:07 +0000
From: Christoph Lameter <cl@linux.com>
Subject: Re: RFC vmstat: On demand vmstat threads
In-Reply-To: <alpine.DEB.2.02.1309201930590.4089@ionos.tec.linutronix.de>
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Sender: owner-linux-mm@kvack.org
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Gilad Ben-Yossef <gilad@benyossef.com>, Tejun Heo <tj@kernel.org>, John Stultz <johnstul@us.ibm.com>, Mike Frysinger <vapier@gentoo.org>, Minchan Kim <minchan.kim@gmail.com>, Hakan Akkan <hakanakkan@gmail.com>, Max Krasnyansky <maxk@qualcomm.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linux-MM <linux-mm@kvack.org>, Peter Zijlstra <peterz@infradead.org>

On Fri, 20 Sep 2013, Thomas Gleixner wrote:

> Now when a cpu becomes isolated we stop the callback scheduling on
> that cpu and assign it to the cpu with the smallest NUMA
> distance. So that cpu will process the data for itself and for the
> newly isolated cpu.

That is not possible for many percpu threads since they rely on running on
a specific cpu for optimization purposes. Running on a different processor
makes these threads racy.

What is needed is to be able to switch these things off and on. Something
on a different cpu may monitor if processing on that specific cpu is
needed or not but it cannot perform the vmstat updates.

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