Changing clock in KVM host may cause VM to hang

Changing clock in KVM host may cause VM to hang

[编码人]

Hi,

My KVM guest OS is Windows 7. If I change the clock in KVM host
(Redhat Enterprise Linux 6), Windows may hang --I can't move mouse in
the VNC desktop. (If I only set clock to be several minutes faster,
then there is no problems. If I set it to be one day faster, then the
problem occurs.)

Does anyone know why it happens? How can we solve it? BTW, is there a
good way to synchronize the clock between the host and the guest?

Thanks,
ff

Re: Changing clock in KVM host may cause VM to hang

[编码人]

Hi,

Does anyone know this issue?

Thanks,
Paul

On Sat, Aug 13, 2011 at 8:10 AM, 编码人 <flypen@gmail.com> wrote:
>
> Hi,
>
> My KVM guest OS is Windows 7. If I change the clock in KVM host
> (Redhat Enterprise Linux 6), Windows may hang --I can't move mouse in
> the VNC desktop. (If I only set clock to be several minutes faster,
> then there is no problems. If I set it to be one day faster, then the
> problem occurs.)
>
> Does anyone know why it happens? How can we solve it? BTW, is there a
> good way to synchronize the clock between the host and the guest?
>
> Thanks,
> ff

Re: Changing clock in KVM host may cause VM to hang

[lidong chen]

2011/8/16 编码人 <flypen@gmail.com>:
> Hi,
>
> Does anyone know this issue?
>
> Thanks,
> Paul
>
> On Sat, Aug 13, 2011 at 8:10 AM, 编码人 <flypen@gmail.com> wrote:
>>
>> Hi,
>>
>> My KVM guest OS is Windows 7. If I change the clock in KVM host
>> (Redhat Enterprise Linux 6), Windows may hang --I can't move mouse in
>> the VNC desktop. (If I only set clock to be several minutes faster,
>> then there is no problems. If I set it to be one day faster, then the
>> problem occurs.)
>>
>> Does anyone know why it happens? How can we solve it? BTW, is there a
>> good way to synchronize the clock between the host and the guest?

you can run ntp client in guest os to synchronize time with host os.

>>
>> Thanks,
>> ff
> --
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>

Re: Changing clock in KVM host may cause VM to hang

[编码人]

Hi, Lidong,

Yes, running ntp client in Guest OS can synchronize the time. But if I
change the clock of the host, the Guest OS may immediately have
problems, and the clock perhaps has no chances to synchronize.

Thanks,
Paul

2011/8/16 lidong chen <chen.lidong.kernel@gmail.com>:
> 2011/8/16 编码人 <flypen@gmail.com>:
>> Hi,
>>
>> Does anyone know this issue?
>>
>> Thanks,
>> Paul
>>
>> On Sat, Aug 13, 2011 at 8:10 AM, 编码人 <flypen@gmail.com> wrote:
>>>
>>> Hi,
>>>
>>> My KVM guest OS is Windows 7. If I change the clock in KVM host
>>> (Redhat Enterprise Linux 6), Windows may hang --I can't move mouse in
>>> the VNC desktop. (If I only set clock to be several minutes faster,
>>> then there is no problems. If I set it to be one day faster, then the
>>> problem occurs.)
>>>
>>> Does anyone know why it happens? How can we solve it? BTW, is there a
>>> good way to synchronize the clock between the host and the guest?
>
> you can run ntp client in guest os to synchronize time with host os.
>
>>>
>>> Thanks,
>>> ff
>> --
>> To unsubscribe from this list: send the line "unsubscribe kvm" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>

Re: Changing clock in KVM host may cause VM to hang

[Xiao Guangrong]

On 08/16/2011 03:50 PM, 编码人 wrote:
> Hi,
> 
> Does anyone know this issue?
> 

Could you describe your environment more detailed please?
- Your host information (32/64, cpuinfo)
- Your guest information (32/64)

And please enable the trace events of kvm to see what happened when
the guest was hanging:

mount -t debugfs none /debug
echo 1 > /debug/tracing/events/kvm/enable
cat /debug/trace

I'll try to reproduce it.

Thanks!