From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Hetze Subject: Clocksource tsc unstable (delta = -4398046474878 ns) Date: Sun, 28 Mar 2010 13:46:35 +0200 Message-ID: <20100328114635.401C730301D3@mail.linux-ag.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: kvm@vger.kernel.org Return-path: Received: from ironport.linux-ag.com ([62.245.157.240]:60419 "EHLO ironport.linux-ag.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753444Ab0C1Lqg (ORCPT ); Sun, 28 Mar 2010 07:46:36 -0400 Received: from localhost (mail.linux-ag.de [62.245.157.206]) by mail.linux-ag.de (Postfix) with ESMTP id 401C730301D3 for ; Sun, 28 Mar 2010 13:46:35 +0200 (CEST) Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: Hi *, this message appeared in the KVM guest kern.log last night: Mar 27 22:35:30 guest kernel: [260041.559462] Clocksource tsc unstable (delta = -4398046474878 ns) The guest is running a 2.6.31-20-generic-pae ubuntu kernel with hrtimer-tune-hrtimer_interrupt-hang-logic.patch applied. If I understand things correct, in kernel/time/clocksource.c clocksource_watchdog() checks all the /sys/devices/system/clocksource/clocksource0/available_clocksource every 0.5sec for an delta of more than 0.0625s. So the tsc must have changed more than one hour within two subsequent calls of clocksource_watchdog. No event in the host nor anything in the guest gives reasonable cause for this step. However, the number 4398046474878 is only 36226 ns away from 4*1024*1024*1024*1024 The guest is an 32 bit system running in a 64 bit host. Is this an possible cause of this strange message? Any other idea what is going wrong here? Maybe this is a hardware bug? Best regards, Sebastian