linux-kernel - Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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Date:	Fri, 17 Aug 2007 10:52:37 +0200
From:	Andi Kleen <ak@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	heiko.carstens@...ibm.com, horms@...ge.net.au,
	linux-kernel@...r.kernel.org, rpjday@...dspring.com,
	netdev@...r.kernel.org, cfriesen@...tel.com,
	akpm@...ux-foundation.org, jesper.juhl@...il.com,
	linux-arch@...r.kernel.org, zlynx@....org, satyam@...radead.org,
	clameter@....com, schwidefsky@...ibm.com,
	Chris Snook <csnook@...hat.com>,
	Herbert Xu <herbert.xu@...hat.com>, davem@...emloft.net,
	wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Friday 17 August 2007 05:42, Linus Torvalds wrote:
> On Fri, 17 Aug 2007, Paul Mackerras wrote:
> > I'm really surprised it's as much as a few K.  I tried it on powerpc
> > and it only saved 40 bytes (10 instructions) for a G5 config.
>
> One of the things that "volatile" generally screws up is a simple
>
> 	volatile int i;
>
> 	i++;

But for atomic_t people use atomic_inc() anyways which does this correctly.
It shouldn't really matter for atomic_t.

I'm worrying a bit that the volatile atomic_t change caused subtle code 
breakage like these delay read loops people here pointed out.
Wouldn't it be safer to just re-add the volatile to atomic_read() 
for 2.6.23? Or alternatively make it asm(), but volatile seems more
proven.

-Andi
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