Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757080Ab0GNSJo (ORCPT ); Wed, 14 Jul 2010 14:09:44 -0400 Received: from terminus.zytor.com ([198.137.202.10]:34023 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754160Ab0GNSJn (ORCPT ); Wed, 14 Jul 2010 14:09:43 -0400 Message-ID: <4C3DFD12.3050700@zytor.com> Date: Wed, 14 Jul 2010 11:08:18 -0700 From: "H. Peter Anvin" 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 Thunderbird/3.0.5 MIME-Version: 1.0 To: Jeremy Fitzhardinge 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 , "H.J. Lu" 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> <4C3DFA88.5020007@goop.org> In-Reply-To: <4C3DFA88.5020007@goop.org> 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: 1131 Lines: 31 [Adding H.J. to the Cc: list] On 07/14/2010 10:57 AM, Jeremy Fitzhardinge wrote: >>> >> 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. > Noone has talked about strict ordering between volatiles and (non-volatile) memory ops in general. I have been talking about volatile to volatile ordering, and I thought I'd been very clear about that. H.J., we're having a debate about the actual semantics of "volatile", especially "asm volatile" in gcc. In particular, I believe that volatile operations should not be possible to reorder with regards to each other, and the kernel depends on that fact. -hpa P.S: gcc 4.4 seems to handle "const volatile" incorrectly, probably by applying CSE to those values. -- 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/