Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761321AbXHPUUn (ORCPT ); Thu, 16 Aug 2007 16:20:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755303AbXHPUUb (ORCPT ); Thu, 16 Aug 2007 16:20:31 -0400 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:52422 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754454AbXHPUU3 (ORCPT ); Thu, 16 Aug 2007 16:20:29 -0400 Date: Thu, 16 Aug 2007 13:20:26 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Chris Snook cc: =?ISO-8859-1?Q?Ilpo_J=E4rvinen?= , Herbert Xu , Paul Mackerras , Satyam Sharma , "Paul E. McKenney" , Stefan Richter , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Linus Torvalds , Netdev , Andrew Morton , ak@suse.de, heiko.carstens@de.ibm.com, David Miller , schwidefsky@de.ibm.com, wensong@linux-vs.org, horms@verge.net.au, wjiang@resilience.com, cfriesen@nortel.com, zlynx@acm.org, rpjday@mindspring.com, jesper.juhl@gmail.com, segher@kernel.crashing.org Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures In-Reply-To: <46C4ABA5.9010804@redhat.com> Message-ID: References: <20070816003948.GY9645@linux.vnet.ibm.com> <18115.44462.622801.683446@cargo.ozlabs.ibm.com> <20070816020042.GA30650@gondor.apana.org.au> <18115.45316.702491.681906@cargo.ozlabs.ibm.com> <18115.52863.638655.658466@cargo.ozlabs.ibm.com> <20070816053945.GB32442@gondor.apana.org.au> <18115.62741.807704.969977@cargo.ozlabs.ibm.com> <20070816070907.GA964@gondor.apana.org.au> <46C4ABA5.9010804@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 845 Lines: 17 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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/