Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754308AbYHKQCm (ORCPT ); Mon, 11 Aug 2008 12:02:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752062AbYHKQCf (ORCPT ); Mon, 11 Aug 2008 12:02:35 -0400 Received: from gw.goop.org ([64.81.55.164]:49897 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751532AbYHKQCe (ORCPT ); Mon, 11 Aug 2008 12:02:34 -0400 Message-ID: <48A06287.8020906@goop.org> Date: Mon, 11 Aug 2008 09:02:15 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Glauber Costa CC: Gerd Hoffmann , Avi Kivity , Marcelo Tosatti , Linux Kernel Mailing List , kvm-devel Subject: Re: Use of barriers in pvclock ABI References: <489CA3DA.1090400@goop.org> <489FE56E.1080707@redhat.com> <5d6222a80808110718i6a600858v7bdb5e08054ebefa@mail.gmail.com> In-Reply-To: <5d6222a80808110718i6a600858v7bdb5e08054ebefa@mail.gmail.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 818 Lines: 21 Glauber Costa wrote: > Okay for guest vcpu, but what about physical cpus? > > IIRC, the checks are there, and so strict, to account for the > possiblity of the vcpu to be migrated to another cpu in the middle of > the > clock reading. > That's fine. As part of rescheduling a vcpu on a new pcpu, the clock record will be updated with the new cpu's parameters, but that update will be complete by the time the vcpu gets rescheduled. The version check and loop still needs to be there, but it will never see an inconsistent (partially updated) clock record. 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/