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

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Message-ID: <48752CF0.20908@goop.org>
Date:	Wed, 09 Jul 2008 14:26:08 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

H. Peter Anvin wrote:
> Either way, I really suspect that the right thing to do is to use 
> negative offsets, with the possible exception of a handful of things 
> (40 bytes or less, perhaps like current) which can get small positive 
> offsets and end up in the "super hot" cacheline.
>
> The sucky part is that I don't believe GNU ld has native support for a 
> "hanging down" section (one which has a fixed endpoint rather than a 
> starting point), so it requires extra magic around the link (or 
> finding some way to do it with linker script functions.) 

If you're going to do another linker pass, you could have a script to 
extract all the percpu symbols and generate a set of derived zero-based 
ones and then link against that.

Or generate a vmlinux with relocations and "relocate" all the percpu 
symbols down to 0.

    J
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