From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760122Ab0JZREl (ORCPT ); Tue, 26 Oct 2010 13:04:41 -0400 Received: from claw.goop.org ([74.207.240.146]:38156 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753137Ab0JZREk (ORCPT ); Tue, 26 Oct 2010 13:04:40 -0400 Message-ID: <4CC70A26.2090200@goop.org> Date: Tue, 26 Oct 2010 10:04:38 -0700 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4 MIME-Version: 1.0 To: Avi Kivity CC: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Marcelo Tosatti , Zachary Amsden , "Xen-devel@lists.xensource.com" Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock References: <1271356648-5108-1-git-send-email-glommer@redhat.com> <1271356648-5108-2-git-send-email-glommer@redhat.com> <4CC6130B.8020908@goop.org> <4CC68DE1.1060604@redhat.com> In-Reply-To: <4CC68DE1.1060604@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/26/2010 01:14 AM, Avi Kivity wrote: > On 10/26/2010 01:30 AM, Jeremy Fitzhardinge wrote: >> Unfortunately this is breaking Xen save/restore: if you restore on a >> host which was booted more recently than the save host, causing the >> system time to be smaller. The effect is that the domain's time leaps >> forward to a fixed point, and stays there until the host catches up to >> the source host... > > Shouldn't save/restore also save the timebase? Xen doesn't guarantee the system time is monotonic across those kinds of events. The domain could maintain its own offset to maintain an illusion of monotonicity, but I think its simpler to just zero last_value on resume. J