linux-kernel - Re: [v7 0/8] Reduce cross CPU IPI interference

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Message-ID: <1328898816.25989.33.camel@laptop>
Date:	Fri, 10 Feb 2012 19:33:36 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	linux-mm@...ck.org, Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Avi Kivity <avi@...hat.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>,
	Milton Miller <miltonm@....com>
Subject: Re: [v7 0/8] Reduce cross CPU IPI interference

On Thu, 2012-02-02 at 10:41 -0500, Chris Metcalf wrote:
> At Tilera we have been supporting a "dataplane" mode (aka Zero Overhead
> Linux - the marketing name).  This is configured on a per-cpu basis, and in
> addition to setting isolcpus for those nodes, also suppresses various
> things that might otherwise run (soft lockup detection, vmstat work,
> etc.).  

See that's wrong.. it starts being wrong by depending on cpuisol and
goes from there.

> The claim is that you need to specify these kinds of things
> per-core since it's not always possible for the kernel to know that you
> really don't want the scheduler or any other interrupt source to touch the
> core, as opposed to the case where you just happen to have a single process
> scheduled on the core and you don't mind occasional interrupts.

Right, so that claim is proven false I think.

>   But
> there's definitely appeal in having the kernel do it adaptively too,
> particularly if it can be made to work just as well as configuring it
> statically. 

I see no reason why it shouldn't work as well or even better.

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