From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Buswell Subject: Re: [PROBLEM] Guest with SMP >=2 with kvm_clock has jumping clock every few seconds Date: Wed, 14 Apr 2010 11:00:14 -0400 Message-ID: <4BC5D87E.5080005@carbonmountain.com> References: <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]:57542 "EHLO smtp.carbonmountain.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755726Ab0DNPAQ (ORCPT ); Wed, 14 Apr 2010 11:00:16 -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 66AA43EA39 for ; Wed, 14 Apr 2010 11:00:15 -0400 (EDT) In-Reply-To: <4BC3647C.80102@carbonmountain.com> Sender: kvm-owner@vger.kernel.org List-ID: Just a follow up on this. The hypervisor had ACPI / ACPI PM clocksource support disabled, as did the guest. This problem occurred with both tsc and jiffies clock sources on the hypervisor. With ACPI enabled and ACPI PM enabled, the clocksources on the hypervisor became hpt and acpi_pm. The guests still using kvm-clock, the clocks come up wrong. But if you set them via rtc0 (hwclock -s), they seem to maintain time ok. Only the first VM that came up exhibited an incorrect uptime. It looks like kvm-clock overrides the setting under RTC -> Set System time from RTC on startup and resume. It might be a good idea to have the guest kernel prefer the RTC setting since its likely to correct. Thanks John Buswell wrote: > 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 CEO, Carbon Mountain LLC http://www.carbonmountain.com