Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757044Ab0GNR5a (ORCPT ); Wed, 14 Jul 2010 13:57:30 -0400 Received: from claw.goop.org ([74.207.240.146]:57874 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752502Ab0GNR53 (ORCPT ); Wed, 14 Jul 2010 13:57:29 -0400 Message-ID: <4C3DFA88.5020007@goop.org> Date: Wed, 14 Jul 2010 10:57:28 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.10) Gecko/20100621 Fedora/3.0.5-1.fc13 Lightning/1.0b2pre Thunderbird/3.0.5 MIME-Version: 1.0 To: "H. Peter Anvin" CC: Linus Torvalds , Peter Palfrader , Avi Kivity , Greg KH , linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Glauber Costa , Zachary Amsden , Marcelo Tosatti Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock References: <20100707124731.GJ15122@anguilla.noreply.org> <4C359D5A.1050906@redhat.com> <20100713102350.GW15122@anguilla.noreply.org> <4C3C68C8.4060409@redhat.com> <20100713141902.GB15122@anguilla.noreply.org> <4C3C8CE5.1080705@redhat.com> <20100713162207.GC15122@anguilla.noreply.org> <4C3C9589.4090602@redhat.com> <4C3C96EC.8060901@redhat.com> <4C3C9839.4090404@redhat.com> <20100713172526.GE15122@anguilla.noreply.org> <4C3CAE8F.10900@goop.org> <4C3CE560.5050701@zytor.com> <4C3CFB8B.1090804@goop.org> <4C3DF1BE.2070404@goop.org> <4C3DF447.1000801@zytor.com> <4C3DF519.6030406@goop.org> <4C3DF7AF.7010402@zytor.com> In-Reply-To: <4C3DF7AF.7010402@zytor.com> X-Enigmail-Version: 1.0.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1215 Lines: 31 On 07/14/2010 10:45 AM, H. Peter Anvin wrote: > On 07/14/2010 10:34 AM, Jeremy Fitzhardinge wrote: > >> On 07/14/2010 10:30 AM, H. Peter Anvin wrote: >> >>> If gcc ever starts reordering volatile operations, including "asm >>> volatile", the kernel will break, and will be unfixable. Just about >>> every single driver will break. All over the kernel we're explicitly or >>> implicitly making the assumption that volatile operations are strictly >>> ordered by the compiler with respect to each other. >>> >> Can you give an example? All the cases I've seen rely on the ordering >> properties of "memory" clobbers, which is sound. (And volatile >> variables are a completely unrelated issue, of course.) >> >> > I/O ports, for example. > Yes, it looks like they should have memory barriers if we want them to be ordered with respect to normal writes; afaict "asm volatile" has never had strict ordering wrt memory ops. Anything else? J -- 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/