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

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Message-ID: <487637DE.1050706@zytor.com>
Date:	Thu, 10 Jul 2008 12:25:02 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Travis <travis@....com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...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

Mike Travis wrote:
> Eric W. Biederman wrote:
> ...
>> Another alternative that almost fares better then a segment with
>> a base of zero is a base of -32K or so.  Only trouble that would get us
>> manually managing the per cpu area size again.
> 
> One thing to remember is the eventual goal is implementing the cpu_alloc
> functions which I think we've agreed has to be "growable".  This means that
> the addresses will need to be virtual to allow the same offsets for all cpus.
> The patchset I have uses 2Mb pages.  This "little" twist might figure into the
> implementation issues that are being discussed.
> 

No, since the *addresses* can be arbitrary.  The current issue is about 
*offsets.*

	-hpa

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