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

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Message-ID: <Pine.LNX.4.64.0708151839140.11520@schroedinger.engr.sgi.com>
Date:	Wed, 15 Aug 2007 18:41:40 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Paul Mackerras <paulus@...ba.org>,
	Satyam Sharma <satyam@...radead.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Chris Snook <csnook@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	netdev@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	ak@...e.de, heiko.carstens@...ibm.com, davem@...emloft.net,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org,
	rpjday@...dspring.com, jesper.juhl@...il.com,
	segher@...nel.crashing.org,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
 architectures

On Wed, 15 Aug 2007, Paul E. McKenney wrote:

> Understood.  My point is not that the impact is precisely zero, but
> rather that the impact on optimization is much less hurtful than the
> problems that could arise otherwise, particularly as compilers become
> more aggressive in their optimizations.

The problems arise because barriers are not used as required. Volatile 
has wishy washy semantics and somehow marries memory barriers with data 
access. It is clearer to separate the two. Conceptual cleanness usually 
translates into better code. If one really wants the volatile then lets 
make it explicit and use

	atomic_read_volatile()
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