time jumps in xen amd64/hvm instance

[Richard Kojedzinszky]

Dear Xen users,

After some experiencing, I've found a soultion to my problem, I just share 
it with you, and hope you wont get issues that I got.

Maybe, all experience is just true for my hardware, but it is not a 
special one, it is a Supermicro PDSMi-LN4 board with a Q6700. I think 
other parameters do not affect.

I had problems with time skews in the domU's, particularly with freebsd 
systems. With HVM instances, hpet should be enabled for the vm, as it 
keeps time ticking very precise. But I had issues, that caused time jumps 
in a short time, and I've found it was related to the dom0's kernel 
message 'Clocksoure tsc unstable'. So then, I've started my xen hypervisor 
with clocksource=pit, and since then (around 1 week) I do not experience 
such time jumps, or time skews.

Regards,


Kojedzinszky Richard
Euronet Magyarorszag Informatikai Zrt.

On Mon, 13 Aug 2012, Richard Kojedzinszky wrote:

> Date: Mon, 13 Aug 2012 10:08:29 +0200 (CEST)
> From: Richard Kojedzinszky <krichy at tvnetwork.hu>
> To: freebsd-xen at freebsd.org
> Subject: Re: time jumps in xen amd64/hvm instance
> 
> Dear developers/users,
>
> I am still facing with time jump problems. Did somebody detect same issues, 
> or only I am doing something wrong. My dom0 is a debian squeeze, my domU is a 
> freebsd-9.0, amd64, kernel compiled by myself.
>
> Currently I cannot find the exact steps needed to reproduce the problem, but 
> unfortunately it happens. Actually, in the past weekend it did also, when the 
> server had lower load than in workdays.
>
> Where should I look further? Any ideas?
>
> Thanks,
>
> Kojedzinszky Richard
> Euronet Magyarorszag Informatikai Zrt.
>
> On Tue, 10 Jul 2012, Richard Kojedzinszky wrote:
>
>> Date: Tue, 10 Jul 2012 20:57:09 +0200 (CEST)
>> From: Richard Kojedzinszky <krichy at tvnetwork.hu>
>> To: freebsd-xen at freebsd.org
>> Subject: Re: time jumps in xen amd64/hvm instance
>> 
>> 
>> just an update, as I remember, this happened to 8.2 bsd in paravirtualized 
>> mode also.
>> 
>> 
>> Kojedzinszky Richard
>> Euronet Magyarorszag Informatikai Zrt.
>> 
>> On Mon, 9 Jul 2012, Richard Kojedzinszky wrote:
>> 
>>> Date: Mon, 9 Jul 2012 21:10:52 +0200 (CEST)
>>> From: Richard Kojedzinszky <krichy at tvnetwork.hu>
>>> To: freebsd-xen at freebsd.org
>>> Subject: time jumps in xen amd64/hvm instance
>>> 
>>> Dear Xen users,
>>> 
>>> I have a strange problem, my hvm instance sometimes jumps time forward. I 
>>> made a little script to monitor this, and I am attaching its result also. 
>>> I have no clues where to look, why this jump happens, but of course it is 
>>> not normal. And as I have kern.securelevel at 2, ntp cannot correct this.
>>> 
>>> Could somebody help?
>>> 
>>> The amd64hvmntp.sh script is run by cron every minute.
>>> 
>>> Thanks in advance,
>>> 
>>> Kojedzinszky Richard
>>> Euronet Magyarorszag Informatikai Zrt.
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