Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761734AbXHXRQD (ORCPT ); Fri, 24 Aug 2007 13:16:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757916AbXHXRPv (ORCPT ); Fri, 24 Aug 2007 13:15:51 -0400 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:57771 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755859AbXHXRPt (ORCPT ); Fri, 24 Aug 2007 13:15:49 -0400 Date: Fri, 24 Aug 2007 10:15:47 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Denys Vlasenko cc: Paul Mackerras , Satyam Sharma , Stefan Richter , Chris Snook , Linux Kernel Mailing List , linux-arch@vger.kernel.org, Linus Torvalds , netdev@vger.kernel.org, Andrew Morton , ak@suse.de, heiko.carstens@de.ibm.com, davem@davemloft.net, 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, Herbert Xu , "Paul E. McKenney" Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures In-Reply-To: <200708241350.45061.vda.linux@googlemail.com> Message-ID: References: <20070809131423.GA9927@shell.boston.redhat.com> <18115.35524.56393.347841@cargo.ozlabs.ibm.com> <200708241350.45061.vda.linux@googlemail.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: 1038 Lines: 22 On Fri, 24 Aug 2007, Denys Vlasenko wrote: > On Thursday 16 August 2007 00:22, Paul Mackerras wrote: > > Satyam Sharma writes: > > In the kernel we use atomic variables in precisely those situations > > where a variable is potentially accessed concurrently by multiple > > CPUs, and where each CPU needs to see updates done by other CPUs in a > > timely fashion. That is what they are for. Therefore the compiler > > must not cache values of atomic variables in registers; each > > atomic_read must result in a load and each atomic_set must result in a > > store. Anything else will just lead to subtle bugs. > > Amen. A "timely" fashion? One cannot rely on something like that when coding. The visibility of updates is insured by barriers and not by some fuzzy notion of "timeliness". - 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/