linux-kernel - Re: RFC: remove __read

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Message-ID: <20071214152454.GR17536@waste.org>
Date:	Fri, 14 Dec 2007 09:24:55 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: RFC: remove __read_mostly

On Thu, Dec 13, 2007 at 11:20:44PM +0100, Adrian Bunk wrote:
> I tried the following patch with a full x86 .config [1]:
> 
> --- a/include/asm-x86/cache.h
> +++ b/include/asm-x86/cache.h
> -#define __read_mostly __attribute__((__section__(".data.read_mostly")))
> +/* #define __read_mostly __attribute__((__section__(".data.read_mostly"))) */
> 
> The result [2,3] was:
> 
> -rwxrwxr-x 1 bunk bunk 46607243 2007-12-13 19:50 vmlinux.old
> -rwxrwxr-x 1 bunk bunk 46598691 2007-12-13 21:55 vmlinux
> 
> It's not a surprise that the kernel can become bigger when __read_mostly 
> gets used, especially in cases where __read_mostly prevents gcc 
> optimizations.
> 
> My question is:
> Is there anywhere in the kernel a case where __read_mostly brings a 
> measurable improvement or can it be removed?

Yes, but perhaps we can put it under CONFIG_BASE_FULL?

-- 
Mathematics is the supreme nostalgia of our time.
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