linux-kernel - Re: Clock jumps

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Message-Id: <4D7E210A-4694-4B6E-B721-6024CE96ABC0@suse.de>
Date:	Wed, 26 May 2010 19:31:15 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Orion Poplawski <orion@...a.nwra.com>
Cc:	Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: Clock jumps


On 26.05.2010, at 19:10, Orion Poplawski wrote:

> On 05/25/2010 12:21 AM, Gleb Natapov wrote:
>> Adding kvm to CC.
>> 
>> On Mon, May 24, 2010 at 04:06:32PM +0000, Orion Poplawski wrote:
>>> I have a KVM virtual machine running 2.6.33.4-95.fc13.x86_64 on a CentOS 5.5
>>> host whose clock jumps about 8-12 hours a couple times a day.  I have no idea
>>> what is causing it.  Fedora 12 and Centos 5.5 KVM machines run fine on the same
>>> host.  Is there any debugging I can enable to see what is jumping the clock?
>>> 
>>> kvm-clock: cpu 0, msr 0:1ba4741, boot clock
>>> kvm-clock: cpu 0, msr 0:1e15741, primary cpu clock
>>> Switching to clocksource kvm-clock
>>> rtc_cmos 00:01: setting system clock to 2010-05-20 16:59:48 UTC (1274374788)
> 
> 
> Thanks, though I don't think it made it there.  I'm also not sure it's completely limited to KVM, though that is the only running system I am currently seeing the problem on.  I also see clock jumps during anaconda installs on physical hardware and apparently they have been present since at least F11.  Might be unrelated though.
> 
> I'm really at a loss of how to debug this though.

Do you have ntpd running inside the guest? I have a bug report lying around about 2.6.33 with kvm-clock jumping in time when ntpd is used: https://bugzilla.novell.com/show_bug.cgi?id=582260

Alex

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