linux-kernel - Re: [RFC 00/15] x86_64: Optimize percpu accesses

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Message-ID: <48764E31.4010408@zytor.com>
Date:	Thu, 10 Jul 2008 14:00:17 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Mike Travis <travis@....com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Christoph Lameter wrote:
> 
> Right. The problem is with the percpu area handled by the linker. That percpu area is used by the boot cpu and later we setup other additional per cpu areas. Those can be placed in an arbitrary way if one goes through a table of pointers to these areas.
> 
> However, that does not work if one calculates the virtual address instead of looking up a physical address.
> 

As far as the linker is concerned, there are two address spaces: VMA, 
which is the offset, and LMA, which is the physical address on where to 
load.  The linker doesn't give a flying hoot about the virtual address, 
since it's completely irrelevant as far as it is concerned; it's nothing 
but a kernel-internal abstraction.

	-hpa

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