linux-kernel - Re: [PATCH 05/10] x86

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Message-ID: <Pine.LNX.4.64.0801021256080.22538@schroedinger.engr.sgi.com>
Date:	Wed, 2 Jan 2008 12:58:45 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <ak@...e.de>
cc:	Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>, tglx@...utronix.de,
	mingo@...hat.com
Subject: Re: [PATCH 05/10] x86_64: Use generic percpu

On Sat, 29 Dec 2007, Andi Kleen wrote:

> Anyways the difference between the x86 percpu.h and the generic one is
> that x86-64 uses a short cut through the PDA to get the current cpu
> offset for the current CPU case. The generic one goes through 
> smp_processor_id()->array reference instead. 

No the patch also uses the pda.

> I would request that this optimization is not being removed
> without suitable replacement in the same patchkit.

The optimization was not removed __my_cpu_offset is used to calculate the 
current offset which is using the pda.

#define __my_cpu_offset read_pda(data_offset)

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