Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757318Ab0GNSVM (ORCPT ); Wed, 14 Jul 2010 14:21:12 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:39419 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756571Ab0GNSVJ convert rfc822-to-8bit (ORCPT ); Wed, 14 Jul 2010 14:21:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=JHOG2sZF5f/XSHs8XSPjyyMSz/vycs3C1OlzQJVvYEoykPbU/Ff80qj1NeYN4q55HY 21U9Rx22oudt+bMLYaq7fHDIHyy7jD0O07extpsANs9iaKIA/a/fTQ4Q1P8DhWsN2xGe fn4SZN7jCwZFQLtArERydlCgKsx2YO/9BvTog= MIME-Version: 1.0 In-Reply-To: <4C3DFD12.3050700@zytor.com> 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> <4C3DFD12.3050700@zytor.com> Date: Wed, 14 Jul 2010 11:18:23 -0700 Message-ID: Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock From: "H.J. Lu" To: "H. Peter Anvin" Cc: Jeremy Fitzhardinge , 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1414 Lines: 44 On Wed, Jul 14, 2010 at 11:08 AM, H. Peter Anvin wrote: > [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. > > There are some discussions on: http://gcc.gnu.org/ml/gcc-patches/2010-06/msg02001.html http://gcc.gnu.org/ml/gcc-patches/2010-07/msg00001.html Are they related? -- H.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/