Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761503AbXIJUyx (ORCPT ); Mon, 10 Sep 2007 16:54:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760513AbXIJUyn (ORCPT ); Mon, 10 Sep 2007 16:54:43 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:57119 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759607AbXIJUyl (ORCPT ); Mon, 10 Sep 2007 16:54:41 -0400 Date: Mon, 10 Sep 2007 13:54:34 -0700 From: "Paul E. McKenney" To: Christoph Lameter Cc: Segher Boessenkool , Paul Mackerras , heiko.carstens@de.ibm.com, horms@verge.net.au, Stefan Richter , Satyam Sharma , Linux Kernel Mailing List , David Miller , Ilpo =?iso-8859-1?Q?J=E4rvinen?= , ak@suse.de, cfriesen@nortel.com, rpjday@mindspring.com, Netdev , jesper.juhl@gmail.com, linux-arch@vger.kernel.org, Andrew Morton , zlynx@acm.org, schwidefsky@de.ibm.com, Chris Snook , Herbert Xu , Linus Torvalds , wensong@linux-vs.org, wjiang@resilience.com Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures Message-ID: <20070910205434.GF11801@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <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: 1104 Lines: 24 On Mon, Sep 10, 2007 at 11:59:29AM -0700, Christoph Lameter wrote: > On Fri, 17 Aug 2007, Segher Boessenkool wrote: > > > "volatile" has nothing to do with reordering. atomic_dec() writes > > to memory, so it _does_ have "volatile semantics", implicitly, as > > long as the compiler cannot optimise the atomic variable away > > completely -- any store counts as a side effect. > > Stores can be reordered. Only x86 has (mostly) implicit write ordering. So > no atomic_dec has no volatile semantics and may be reordered on a variety > of processors. Writes to memory may not follow code order on several > processors. The one exception to this being the case where process-level code is communicating to an interrupt handler running on that same CPU -- on all CPUs that I am aware of, a given CPU always sees its own writes in order. 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/