linux-kernel - Re: [PATCH v6 0/8] Reduce cross CPU IPI interference

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Date:	Mon, 9 Jan 2012 12:57:49 -0500
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	<linux-kernel@...r.kernel.org>, Christoph Lameter <cl@...ux.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.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.org>,
	Kosaki Motohiro <kosaki.motohiro@...il.com>
Subject: Re: [PATCH v6 0/8] Reduce cross CPU IPI interference

On 1/8/2012 11:26 AM, Gilad Ben-Yossef wrote:
> We have lots of infrastructure in place to partition a multi-core systems
> such that we have a group of CPUs that are dedicated to specific task:
> cgroups, scheduler and interrupt affinity and cpuisol boot parameter.
> Still, kernel code will some time interrupt all CPUs in the system via IPIs
> for various needs. These IPIs are useful and cannot be avoided altogether,
> but in certain cases it is possible to interrupt only specific CPUs that
> have useful work to do and not the entire system.
>
> This patch set, inspired by discussions with Peter Zijlstra and Frederic
> Weisbecker when testing the nohz task patch set, is a first stab at trying
> to explore doing this by locating the places where such global IPI calls
> are being made and turning a global IPI into an IPI for a specific group
> of CPUs.  The purpose of the patch set is to get feedback if this is the
> right way to go for dealing with this issue and indeed, if the issue is
> even worth dealing with at all. Based on the feedback from this patch set
> I plan to offer further patches that address similar issue in other code
> paths.
>
> The patch creates an on_each_cpu_mask and on_each_cpu_conf infrastructure 
> API (the former derived from existing arch specific versions in Tile and 
> Arm) and and uses them to turn several global IPI invocation to per CPU 
> group invocations.

Acked-by: Chris Metcalf <cmetcalf@...era.com>

(To be fair, mostly this acks the proposed infrastructure, and moving the
functions out of the tile architecture and into the generic code; I not
expert enough at slub or the invalidate_bh_lrus path to ack those changes,
other than to say I like how they look.)

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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