linux-kernel - Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead

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Message-Id: <20071101.142809.179954273.davem@davemloft.net>
Date:	Thu, 01 Nov 2007 14:28:09 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	clameter@....com
Cc:	dada1@...mosbay.com, akpm@...ux-foundation.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	mathieu.desnoyers@...ymtl.ca, penberg@...helsinki.fi
Subject: Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu
 access overhead

From: Christoph Lameter <clameter@....com>
Date: Thu, 1 Nov 2007 05:57:12 -0700 (PDT)

> That is basically what IA64 is doing but it not usable because you would 
> have addresses that mean different things on different cpus. List head
> for example require back pointers. If you put a listhead into such a per 
> cpu area then you may corrupt another cpus per cpu area.

Indeed, but as I pointed out in another mail it actually works if you
set some rules:

1) List insert and delete is only allowed on local CPU lists.

2) List traversal is allowed on remote CPU lists.

I bet we could get all of the per-cpu users to abide by this
rule if we wanted to.

The remaining issue with accessing per-cpu areas at multiple virtual
addresses is D-cache aliasing.
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