linux-kernel - RFC: remove __read

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Message-ID: <20071213222044.GH21616@stusta.de>
Date:	Thu, 13 Dec 2007 23:20:44 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	linux-kernel@...r.kernel.org
Cc:	linux-arch@...r.kernel.org
Subject: RFC: remove __read_mostly

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?

cu
Adrian

[1] mostly allyesconfig with CONFIG_MODULES=n
[2] vmlinux.old is the unpatched kernel
[3] gcc 4.2 was used

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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