Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753218AbXHISp0 (ORCPT ); Thu, 9 Aug 2007 14:45:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753430AbXHISoy (ORCPT ); Thu, 9 Aug 2007 14:44:54 -0400 Received: from gate.crashing.org ([63.228.1.57]:51062 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757206AbXHISow (ORCPT ); Thu, 9 Aug 2007 14:44:52 -0400 In-Reply-To: <46BB3ECF.2070100@redhat.com> References: <20070809132442.GA13042@shell.boston.redhat.com> <20070809143255.GA8424@linux.vnet.ibm.com> <46BB2A5A.5090006@redhat.com> <20070809150445.GB8424@linux.vnet.ibm.com> <46BB31A6.4080507@redhat.com> <3bfabd7472d6f019aa1880b14013f7a1@kernel.crashing.org> <46BB3ECF.2070100@redhat.com> Mime-Version: 1.0 (Apple Message framework v623) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <1abc2c621d6b62b3ac9f489d4d18806a@kernel.crashing.org> Content-Transfer-Encoding: 7bit Cc: wjiang@resilience.com, cfriesen@nortel.com, wensong@linux-vs.org, heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, ak@suse.de, netdev@vger.kernel.org, paulmck@linux.vnet.ibm.com, horms@verge.net.au, akpm@linux-foundation.org, linux-arch@vger.kernel.org, jesper.juhl@gmail.com, torvalds@linux-foundation.org, zlynx@acm.org, rpjday@mindspring.com, schwidefsky@de.ibm.com, davem@davemloft.net From: Segher Boessenkool Subject: Re: [PATCH 1/24] make atomic_read() behave consistently on alpha Date: Thu, 9 Aug 2007 20:38:24 +0200 To: Chris Snook X-Mailer: Apple Mail (2.623) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1140 Lines: 28 >> The only safe way to get atomic accesses is to write >> assembler code. Are there any downsides to that? I don't >> see any. > > The assumption that aligned word reads and writes are atomic, and that > words are aligned unless explicitly packed otherwise, is endemic in > the kernel. No sane compiler violates this assumption. It's true > that we're not portable to insane compilers after this patch, but we > never were in the first place. You didn't answer my question: are there any downsides to using explicit coded-in-assembler accesses for atomic accesses? You can handwave all you want that it should "just work" with volatile accesses, but volatility != atomicity, volatile in C is really badly defined, GCC never officially gave stronger guarantees, and we have a bugzilla full of PRs to show what a minefield it is. So, why not use the well-defined alternative? Segher - 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/