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

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Message-ID: <487522A8.60906@zytor.com>
Date:	Wed, 09 Jul 2008 16:42:16 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	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

Jeremy Fitzhardinge wrote:
> 
> No, you do it the same as i386.  You set the segment base to be 
> percpu_area-__per_cpu_start, and then just refer to %gs:per_cpu__foo 
> directly.  You can use rip-relative addressing to make it a smaller 
> addressing mode too:
> 
>   0:    65 89 05 00 00 00 00     mov    %eax,%gs:0(%rip)        # 0x7
> 

Thinking about this some more, I don't know if it would make sense to 
put the x86-64 stack canary at the *end* of the percpu area, and 
otherwise use negative offsets.  That would make sure they were readily 
reachable from %rip-based references from within the kernel text area.

	-hpa
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