linux-kernel - Re: [pull request] getting rid of _

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Date:	Sat, 25 Oct 2008 09:59:25 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [pull request] getting rid of __cpuinit

On Fri, Oct 24, 2008 at 02:20:56PM -0700, Arjan van de Ven wrote:
> Hi Linus,
> 
> this is one of those pull requests for which the best timing is likely at the 
> end of the merge window due to touching a large number of files in a trivial way.
> In fact, 6 of the 8 patches were done via regexps:
> 
> find -name "*.c" | xargs sed -i "s/^__cpuinit //g"
> find arch/ -name "*.h" | xargs sed -i "s/ __cpuinit//g"
> find -name "*.c" | xargs sed -i "s/ __cpuinit$//g"
> find -name "*.c" | xargs sed -i "s/ __cpuinitdata//g"
> find -name "*.c" | xargs sed -i "s/ __cpuexit / /g"
> find -name "*.c" | xargs sed -i "s/ __cpuinit / /g"
> 
> (I suppose asking for a "git sed" is too much to do...)
> 
> The point of this series is to get rid of __cpuinit. (I'll be working on other __XXXXinit after this)
> __cpuinit is a NOOP for CONFIG_HOTPLUG_CPU, which on for just about anybody in practice 
> (in fact I had to disable 6 common options to even be ABLE to turn it off for size testing) 
> and all distros also ship with it enabled.
> 
> Yet it's a rather error prone construct since the rules of this sort of __XXXXinit thing are
> rather complex and convoluted.. better to just get rid of it entirely.
> 
> As for the code size effect, after I spent a bunch of time cursing and trying to find out
> how to disable HOTPLUG_CPU, I managed to get an x86-64 build that actually shows how much space 
> we ACTUALLY save with all the __cpuinit's in the tree... it's less than 2Kb. That is, if you manage
> to turn it actually off.
> 
>    text	   data	    bss	    dec	    hex	filename
> 4618096	1358684	 848588	6825368	 682598	vmlinux.before
> 4619965	1356908	 848716	6825589  682675	vmlinux.after

The interesting number here is the size of the cpuinit/cpuexit sections.
cpuinit sections are discarded after init and cpuexit sections are discarded
if you do not use modules.

Can you share these numbers with us?

	Sam
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