linux-kernel - Re: Clock jumps

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Message-ID: <4BFDA6F4.1080101@cora.nwra.com>
Date:	Wed, 26 May 2010 16:55:48 -0600
From:	Orion Poplawski <orion@...a.nwra.com>
To:	Alexander Graf <agraf@...e.de>
CC:	Gleb Natapov <gleb@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: Clock jumps

On 05/26/2010 11:31 AM, Alexander Graf wrote:
>
> 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
>

That bug looks just like what I'm seeing.  I even see the soft lockup messages 
sometimes as well.  May actually be seeing it with a Fedora 12 guest as well - 
but it results in a hard hang.

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  orion@...a.nwra.com
Boulder, CO 80301              http://www.cora.nwra.com
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