Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762965AbXHQBCv (ORCPT ); Thu, 16 Aug 2007 21:02:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753716AbXHQBCi (ORCPT ); Thu, 16 Aug 2007 21:02:38 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:52343 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752823AbXHQBCg (ORCPT ); Thu, 16 Aug 2007 21:02:36 -0400 Date: Thu, 16 Aug 2007 18:02:32 -0700 From: "Paul E. McKenney" To: Christoph Lameter Cc: Chris Snook , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Herbert Xu , Paul Mackerras , Satyam Sharma , 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 Message-ID: <20070817010232.GK16957@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <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 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1025 Lines: 22 On Thu, Aug 16, 2007 at 01:20:26PM -0700, Christoph Lameter wrote: > 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. Yep. Or you can use atomic_dec_return() instead of using a barrier. Thanx, Paul - 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/