From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nadav Har'El Subject: Monotonic clock with KVM pv-clock Date: Mon, 20 Jan 2014 11:56:56 +0200 Message-ID: <20140120095656.GA1282@fermat.math.technion.ac.il> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: mtosatti@redhat.com, kvm@vger.kernel.org Return-path: Received: from mailgw12.technion.ac.il ([132.68.225.12]:49080 "EHLO mailgw12.technion.ac.il" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752710AbaATKHF (ORCPT ); Mon, 20 Jan 2014 05:07:05 -0500 Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: Hi, I'm trying to figure out how a guest OS can get a monotonic clock using KVM's paravirtual clock. At first, I thought that the clock I get using KVM_SYSTEM_TIME is a monotonic clock, based on the host's monotonic clock. But I'm no longer sure this is actually done correctly: 1. What happens on live migration? On the new host, will the KVM_SYSTEM_TIME continue from the same point? Or will it jump because KVM_WALL_CLOCK (the wall time during boot) is different on the new host? 2. What happens when the wall-clock time is set on the host? I was hoping that only KVM_WALL_CLOCK changes and KVM_SYSTEM_TIME doesn't, but am no longer sure this is actually the case. If KVM_SYSTEM_TIME is not a correct way to get a monotonic paravirtual clock from KVM, is there a correct way? Thanks, Nadav. -- Nadav Har'El | Monday, Jan 20 2014, 19 Shevat 5774 nyh@math.technion.ac.il |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |Diplomat: A man who always remembers a http://nadav.harel.org.il |woman's birthday but never her age.