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

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Date:	Thu, 10 Jul 2008 10:53:00 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Christoph Lameter wrote:
>> The nice thing about the non-zero-based scheme i386 uses is that setting
>> gs-base to zero means that percpu variables accesses get directly to the
>> prototype percpu data area, which simplifies boot time setup (which is
>> doubly awkward on 32-bit because you need to generate a GDT entry rather
>> than just load an MSR as you do in 64-bit).
>>     
>
> Great but it causes trouble in other ways as discussed.

What other trouble?  It works fine.

>  Its best to consistently access
> per cpu variables using the segment registers.
>   


It is, but initially the segment base is 0, so just using a percpu 
variable does something sensible from the start with no special setup.

    J
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