linux-kernel - Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile_

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Message-Id: <200707231818.00547.ak@suse.de>
Date:	Mon, 23 Jul 2007 18:18:00 +0200
From:	Andi Kleen <ak@...e.de>
To:	Satyam Sharma <ssatyam@....iitk.ac.in>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__

On Monday 23 July 2007 18:06:03 Satyam Sharma wrote:
> From: Satyam Sharma <ssatyam@....iitk.ac.in>
> 
> [7/8] i386: bitops: Kill needless usage of __asm__ __volatile__
> 
> Another oddity I noticed in this file. The semantics of __volatile__
> when used to qualify inline __asm__ are that the compiler will not
> (1) elid, or, (2) reorder, or, (3) intersperse, our inline asm with
> the rest of the generated code.
> 
> However, we do not want these guarantees in the unlocked variants of the
> bitops functions. 

I thought so too and did a similar transformation while moving
some string functions out of line. After that recent misadventure
I would be very very careful with this.

Overall I'm sorry to say, but the risk:gain ratio of this
patch is imho totally out of whack.

It took a long time to get bitops.h correct and as far as we know
it is compiled correctly currently. You risk all at for very dubious
improvements.

-Andi



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