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

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Message-ID: <4876791F.40603@zytor.com>
Date:	Thu, 10 Jul 2008 17:03:27 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	"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

Jeremy Fitzhardinge wrote:
> 
> Percpu on i386 hasn't been a point of discussion.  It works fine, and 
> has been working fine for a long time.  The same mechanism would work 
> fine on x86-64.  Its only "issue" is that it doesn't support the broken 
> gcc abi for stack-protector.
> 
> The problem is all zero-based percpu on x86-64.
> 

Well, x86-64 has *two* issues: limited range of offsets (regardless of 
if we do RIP-relative or not), and the stack-protector ABI.

I'm still trying to reproduce Mike's setup, but I suspect it can be 
switched to RIP-relative for the fixed-offset (static) stuff; for the 
dynamic stuff it's all via pointers anyway so the offsets don't matter.

	-hpa
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