From mboxrd@z Thu Jan  1 00:00:00 1970
From: "David S. Ahern" <daahern@cisco.com>
Subject: RHEL5.5, 32-bit VM repeatedly locks up due to kvmclock
Date: Fri, 23 Apr 2010 11:08:22 -0600
Message-ID: <4BD1D406.1040508@cisco.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
To: kvm-devel <kvm@vger.kernel.org>
Return-path: <kvm-owner@vger.kernel.org>
Received: from sj-iport-6.cisco.com ([171.71.176.117]:35839 "EHLO
	sj-iport-6.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1758302Ab0DWRIX (ORCPT <rfc822;kvm@vger.kernel.org>);
	Fri, 23 Apr 2010 13:08:23 -0400
Received: from [10.89.10.142] ([10.89.10.142])
	by sj-core-5.cisco.com (8.13.8/8.14.3) with ESMTP id o3NH8MdV008047
	for <kvm@vger.kernel.org>; Fri, 23 Apr 2010 17:08:23 GMT
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

After a few days of debugging I think kvmclock is the source of lockups
for a RHEL5.5-based VM. The VM works fine on one host, but repeatedly
locks up on another.

Server 1 - VM locks up repeatedly
-- DL580 G5
-- 4 quad-core X7350 processors at 2.93GHz
-- 48GB RAM

Server 2 - VM works just fine
-- DL380 G6
-- 2 quad-core E5540 processors at 2.53GHz
-- 24GB RAM

Both host servers are running Fedora Core 12, 2.6.32.11-99.fc12.x86_64
kernel. I have tried various versions of qemu-kvm -- the version in
FC-12 and the version for FC-12 in virt-preview. In both cases the
qemu-kvm command line is identical.

VM
- RHEL5.5, PAE kernel (also tried standard 32-bit)
- 2 vcpus
- 3GB RAM
- virtio network and disk

When the VM locks up both vcpu threads are spinning at 100%. Changing
the clocksource to jiffies appears to have addressed the problem.

David