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Re: [PATCH 2/2] Alchemy: provide cpu feature overrides.

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: [PATCH 2/2] Alchemy: provide cpu feature overrides.
From: Manuel Lauss <mano@roarinelk.homelinux.net>
Date: Tue, 23 Dec 2008 17:29:54 +0100
Cc: Linux-MIPS <linux-mips@linux-mips.org>
In-reply-to: <20081223143909.GD5981@linux-mips.org>
Organization: Private
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1229973668-18182-1-git-send-email-mano@roarinelk.homelinux.net> <1229973668-18182-2-git-send-email-mano@roarinelk.homelinux.net> <20081223143909.GD5981@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
On Tue, 23 Dec 2008 15:39:09 +0100
Ralf Baechle <ralf@linux-mips.org> wrote:

> On Mon, Dec 22, 2008 at 08:21:08PM +0100, Manuel Lauss wrote:
> 
> > Add cpu feature override constants for Alchemy.
> > 
> > Code generated for Alchemy does not use all MIPS32r1 features.  Add cpu
> > feature overrides tailored for Alchemy chips and help GCC create better
> > code.  As a nice sideeffect the size of the resulting kernel is reduced
> > by a few kilobytes (~200kB for a non-modular db1200 devboard build).
> 
> The enormous size difference is probably 99% due to atomic and bitops
> which exist in LL/SC and non-LL/SC versions and without the header gcc
> will expand the inline function each time.  That will hurt, also
> performance.  Also the big size difference suggests that we may want to
> outline some or all of these functions.

You are of course correct:

   text    data     bss     dec     hex filename                                
                                                                                
3890074  124400  436528 4451002  43eaba vmlinux                                 
                                                                                
3890070  124400  436528 4450998  43eab6 vmlinux+mips32r1
3690742  124396  436528 4251666  40e012 vmlinux++llsc
3666386  124332  436528 4227246  4080ae vmlinux+++all

-- ml.

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