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Message-ID: <Pine.LNX.4.64.0708161319000.17777@schroedinger.engr.sgi.com>
Date: Thu, 16 Aug 2007 13:20:26 -0700 (PDT)
From: Christoph Lameter <clameter@....com>
To: Chris Snook <csnook@...hat.com>
cc: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
Herbert Xu <herbert@...dor.apana.org.au>,
Paul Mackerras <paulus@...ba.org>,
Satyam Sharma <satyam@...radead.org>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Stefan Richter <stefanr@...6.in-berlin.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arch@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Netdev <netdev@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, ak@...e.de,
heiko.carstens@...ibm.com, David Miller <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
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all
architectures
On Thu, 16 Aug 2007, Chris Snook wrote:
> atomic_dec() already has volatile behavior everywhere, so this is semantically
> okay, but this code (and any like it) should be calling cpu_relax() each
> iteration through the loop, unless there's a compelling reason not to. I'll
> allow that for some hardware drivers (possibly this one) such a compelling
> reason may exist, but hardware-independent core subsystems probably have no
> excuse.
No it does not have any volatile semantics. atomic_dec() can be reordered
at will by the compiler within the current basic unit if you do not add a
barrier.
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