linux-kernel - Re: [PATCH 8/8] Convert PDA into the percpu section

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Message-ID: <45EDB2B5.4000506@goop.org>
Date:	Tue, 06 Mar 2007 10:28:05 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Zachary Amsden <zach@...are.com>,
	Jeremy Fitzhardinge <jeremy@...source.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [PATCH 8/8] Convert PDA into the percpu section

Rusty Russell wrote:
> Currently x86 (similar to x84-64) has a special per-cpu structure
> called "i386_pda" which can be easily and efficiently referenced via
> the %fs register.  An ELF section is more flexible than a structure,
> allowing any piece of code to use this area.  Indeed, such a section
> already exists: the per-cpu area.
>
> So this patch
> (1) Removes the PDA and uses per-cpu variables for each current member.
> (2) Replaces the __KERNEL_PDA segment with __KERNEL_PERCPU.
> (3) Creates a per-cpu mirror of __per_cpu_offset called this_cpu_off, which
>     can be used to calculate addresses for this CPU's variables.
> (4) Moves the boot cpu's GDT/percpu setup to smp_prepare_boot_cpu(),
>     immediately after the per-cpu areas are allocated.
>
> The result is one less x86-specific concept.
>   

Looks good.  I think you can drop x86_add/sub/or_percpu; there are no users.

Signed-off-by: Jeremy Fitzhardinge <jeremy@...source.com>

    J
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