From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Buswell Subject: [PROBLEM] Guest with SMP >=2 with kvm_clock has jumping clock every few seconds Date: Mon, 12 Apr 2010 14:20:44 -0400 Message-ID: <4BC3647C.80102@carbonmountain.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: kvm@vger.kernel.org Return-path: Received: from smtp.carbonmountain.com ([74.207.244.159]:58557 "EHLO smtp.carbonmountain.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753130Ab0DLSpS (ORCPT ); Mon, 12 Apr 2010 14:45:18 -0400 Received: from john-buswells-macbook-pro.local (cpe-184-57-92-238.columbus.res.rr.com [184.57.92.238]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: buswellj) by smtp.carbonmountain.com (Postfix) with ESMTP id EE81A3EA39 for ; Mon, 12 Apr 2010 14:20:45 -0400 (EDT) Sender: kvm-owner@vger.kernel.org List-ID: I ran into the problem below running 2.6.33.2: Problem: KVM guest running Linux 2.6.33.2 with kvm_clock as the clock source and more than 1 virtual CPU has the clock jumping forward 1 hour, 13 minutes and 17 seconds (consistently) Hardware: AMD Athlon Dual Core 4850e @ 2511.769 MHz I can reproduce this consistently, and it does not happen on the same machine if I launch the same KVM guest with -smp 1. With RTC compiled into the kernel you can see that its just clock, the localtime was set to UTC: Running the following in a loop: cat /sys/class/rtc/rtc0/time ; date You see: 18:07:49 Mon Apr 12 18:07:49 UTC 2010 18:08:21 Mon Apr 12 19:21:49 UTC 2010 18:08:21 Mon Apr 12 18:08:22 UTC 2010 The load average on the system is 0, the guest is doing nothing but running init. It happens regardless of whether I run one guest or over 10 guests on the same system. I can easily reproduce this issue, so if you need someone to test patches etc, I can easily do that. Thanks -- John Buswell http://www.carbonmountain.com