Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937037AbXHNW6n (ORCPT ); Tue, 14 Aug 2007 18:58:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S936227AbXHNW42 (ORCPT ); Tue, 14 Aug 2007 18:56:28 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:53605 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935463AbXHNW4Y (ORCPT ); Tue, 14 Aug 2007 18:56:24 -0400 Date: Wed, 15 Aug 2007 04:38:54 +0530 (IST) From: Satyam Sharma X-X-Sender: satyam@enigma.security.iitk.ac.in To: Christoph Lameter cc: Chris Snook , Linux Kernel Mailing List , linux-arch@vger.kernel.org, torvalds@linux-foundation.org, 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 Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures In-Reply-To: Message-ID: References: <20070809131423.GA9927@shell.boston.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: 1703 Lines: 35 On Tue, 14 Aug 2007, Christoph Lameter wrote: > On Thu, 9 Aug 2007, Chris Snook wrote: > > > This patchset makes the behavior of atomic_read uniform by removing the > > volatile keyword from all atomic_t and atomic64_t definitions that currently > > have it, and instead explicitly casts the variable as volatile in > > atomic_read(). This leaves little room for creative optimization by the > > compiler, and is in keeping with the principles behind "volatile considered > > harmful". > > volatile is generally harmful even in atomic_read(). Barriers control > visibility and AFAICT things are fine. Frankly, I don't see the need for this series myself either. Personal opinion (others may differ), but I consider "volatile" to be a sad / unfortunate wart in C (numerous threads on this list and on the gcc lists/bugzilla over the years stand testimony to this) and if we _can_ steer clear of it, then why not -- why use this ill-defined primitive whose implementation has often differed over compiler versions and platforms? Granted, barrier() _is_ heavy-handed in that it makes the optimizer forget _everything_, but then somebody did post a forget() macro on this thread itself ... [ BTW, why do we want the compiler to not optimize atomic_read()'s in the first place? Atomic ops guarantee atomicity, which has nothing to do with "volatility" -- users that expect "volatility" from atomic ops are the ones who must be fixed instead, IMHO. ] - 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/