Re: [Xen-users] Resolve "Time went backwards" problem by using jiffies as clocksource

["Matthew Law" <matt@xxxxxxxxxxxxxxxxxx>]

Hi Daniel,

I'm sure someone has the answer - just not likely to arrive to quickly at
this time of year and a weekend ;-)

I ran in to this too (I'm a relative Xen newbie) and my experience of this
bug is that it is a problem which is inherent in the xenified debian
kernels.  They appear to use some of the backports from opensuse and there
appears to be an issue with the way they have been used in debian which
means the kernel clock sync doesn't work properly.

You can detach the clock sync from the dom0 and do it in the domU with ntp
(as per the debain wiki doc) or, build your own kernel using the vanilla
xen kernel sources (which works, but is a pain).  I opted for the former. 
I get the impression that this won't be fixed for a while in debian stable
as, like so many others, they are concentrating on kvm over xen.

There may be other options.  I am sure others will chime in if there are.

Good luck,

Matt.

On Sun, January 3, 2010 4:56 pm, Daniel Lam wrote:
> On Mon, Jan 4, 2010 at 3:49 AM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
>
>> On Mon, Jan 04, 2010 at 03:44:34AM +1100, Daniel Lam wrote:
>> >    Hi All - so I guess nobody has the answers to these questions?
>> >    Is there somewhere I can ask, perhaps the developers list?
>> >
>>
>> Have you tried using newer Xen hypervisor?
>> Xen 3.4.2 is the latest stable release.
>>
>> Also, did you try different dom0/domU kernel versions?
>>
>> -- Pasi
>>
>>
> Thanks for prompt reply.
>
> I *think* I have the latest stable version - I installed Xen by running
>
>    apt-get install xen-linux-system-2.6.26-2-xen-686
>
> on Debian 5.0 Lenny. And no I haven't tried different dom0/domU
> kernel versions. I have only been playing around with Debian 5.0 Lenny,
> as dom0 and domU.
>
> Are you suggesting that using xen as clocksource should work
> on latest stable versions?
>
> And for the record I'm experimenting on a Dell Optiplex GX520 with 2gb
> ram.
>
> Daniel
>
>>    Daniel
>> >    ---------- Forwarded message ----------
>> >    From: Daniel Lam <[1]daniel@xxxxxxxxxxxxxxxx>
>> >    To: [2]xen-users@xxxxxxxxxxxxxxxxxxx
>> >    Date: Sat, 2 Jan 2010 17:20:12 +1100
>> >    Subject: [Xen-users] Resolve "Time went backwards" problem by using
>> >    jiffies as clocksource
>> >    Hi All,
>> >    I'm new to Xen and... Happy New Year!
>> >    After restarting dom-0, my dom-u prints this in console once every
>> second,
>> >    [55082.616234] __ratelimit: 1503 messages suppressed
>> >    [55082.616234] clocksource/0: Time went backwards: ret=380ab26c53a
>> >    I resolved this by following the instructions in
>> >    "[3]http://wiki.debian.org/Xen";,
>> >    which is basically changing clocksource to "jiffies".
>> >    Now the problem has gone away, I'm wondering if somebody can help
>> me:
>> >    1. Is domain-0 not able to set the system time of domain-u the root
>> cause?
>> >        I can see this error in console "Unable to set System Clock to:
>> <a
>> >    datetime value>",
>> >        even after I changed clocksource to "jiffies".
>> >    2. Why can't domain-0 set the date of the domain-u?
>> >    3. If this is the only way to go (using jiffies clocksource), I
>> will
>> have
>> >    to sync
>> >        the domain-u system time manually using something like ntpd?
>> >    Thanks!
>> >    cheers,
>> >    Daniel
>> >
>> > References
>> >
>> >    Visible links
>> >    1. mailto:daniel@xxxxxxxxxxxxxxxx
>> >    2. mailto:xen-users@xxxxxxxxxxxxxxxxxxx
>> >    3. http://wiki.debian.org/Xen


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