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

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Message-ID: <487504A8.5040000@linux-foundation.org>
Date:	Wed, 09 Jul 2008 13:34:16 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Mike Travis <travis@....com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>, Jack Steiner <steiner@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Jeremy Fitzhardinge wrote:

> Eh?  Yes they will.  That's the whole point of making the pda a percpu
> variable itself.  You can use %gs:<small> to get to the pda, and
> %gs:<larger> to get to percpu variables.  Converting pda->percpu will
> just have the effect of increasing the %gs offset into the percpu space.

Right that is what this patchset does.

> This project isn't interesting to me unless per-cpu variables are
> directly accessible off %gs.

Maybe I misunderstood but it seems that you proposed to convert individual members of the pda structure (which uses GS) to per cpu variables (which without this patchset cannot use GS).

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