linux-kernel - Re: RFC vmstat: On demand vmstat threads

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Message-ID: <000001414b5ebafe-a82f870f-283a-4210-a1d8-4035e2720c4f-000000@email.amazonses.com>
Date:	Mon, 23 Sep 2013 15:10:07 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Tejun Heo <tj@...nel.org>, John Stultz <johnstul@...ibm.com>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux-MM <linux-mm@...ck.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: RFC vmstat: On demand vmstat threads

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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