linux-kernel - Re: [PATCH 1/3] x86-64: Convert the PDA to percpu.

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Date:	Sat, 27 Dec 2008 11:41:23 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Brian Gerst <brgerst@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Alexander van Heukelum <heukelum@...lshack.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86-64: Convert the PDA to percpu.


(Cc:-ed a few more people who might be interested in this)

* Brian Gerst <brgerst@...il.com> wrote:

> This patch makes the PDA a normal per-cpu variable, allowing the
> removal of the special allocator code.  %gs still points to the
> base of the PDA.
> 
> Tested on a dual-core AMD64 system.
> 
> Signed-off-by: Brian Gerst <brgerst@...il.com>
> ---
>  arch/x86/include/asm/pda.h     |    3 --
>  arch/x86/include/asm/percpu.h  |    3 --
>  arch/x86/include/asm/setup.h   |    1 -
>  arch/x86/kernel/cpu/common.c   |    6 ++--
>  arch/x86/kernel/dumpstack_64.c |    8 ++--
>  arch/x86/kernel/head64.c       |   23 +------------
>  arch/x86/kernel/irq.c          |    2 +-
>  arch/x86/kernel/nmi.c          |    2 +-
>  arch/x86/kernel/setup_percpu.c |   70 ++++++++--------------------------------
>  arch/x86/kernel/smpboot.c      |   58 +--------------------------------
>  arch/x86/xen/enlighten.c       |    2 +-
>  arch/x86/xen/smp.c             |   12 +------
>  12 files changed, 27 insertions(+), 163 deletions(-)

the simplification factor is significant. I'm wondering, have you measured 
the code size impact of this on say the defconfig x86 kernel? That will 
generally tell us how much worse optimizations the compiler does under 
this scheme.

	Ingo
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