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Message-ID: <20070816200756.GF16957@linux.vnet.ibm.com>
Date: Thu, 16 Aug 2007 13:07:56 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Christoph Lameter <clameter@....com>
Cc: Paul Mackerras <paulus@...ba.org>,
Satyam Sharma <satyam@...radead.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
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
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures
On Thu, Aug 16, 2007 at 11:54:54AM -0700, Christoph Lameter wrote:
> On Thu, 16 Aug 2007, Paul Mackerras wrote:
> > So I don't see any good reason to make the atomic API more complex by
> > having "volatile" and "non-volatile" versions of atomic_read. It
> > should just have the "volatile" behaviour.
>
> If you want to make it less complex then drop volatile which causes weird
> side effects without solving any problems as you just pointed out.
The other set of problems are communication between process context
and interrupt/NMI handlers. Volatile does help here. And the performance
impact of volatile is pretty near zero, so why have the non-volatile
variant?
Thanx, Paul
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