linux-kernel - Re: [patch 1/2] i386: use asm() like the other atomic operations already do.

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Message-ID: <46C3319F.4050809@redhat.com>
Date:	Wed, 15 Aug 2007 13:02:23 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Andi Kleen <ak@...e.de>, sebastian@...akpoint.cc,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] i386: use asm() like the other atomic operations
 already do.

Herbert Xu wrote:
> Andi Kleen <ak@...e.de> wrote:
>>> My config with march=pentium-m and gcc (GCC) 4.1.2 (Gentoo 4.1.2):
>>>   text    data     bss     dec     hex filename
>>> 3434150  249176  176128 3859454  3ae3fe atomic_normal/vmlinux
>>> 3435308  249176  176128 3860612  3ae884 atomic_inlineasm/vmlinux
>> What is the difference between atomic_normal and atomic_inlineasm? 
> 
> The inline asm stops certain optimisations from occuring.
> 
> I'm still unconvinced why we need this because nobody has
> brought up any examples of kernel code that legitimately
> need this.

There's plenty of kernel code that *wants* this though.  If we can 
reduce the need for register-clobbering barriers, shrink our binaries, 
shrink our code, improve performance, and avoid heisenbugs, I think it's 
a win, whether or not we *need* it.

	-- Chris
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