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

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Subject: Re: [Xen-users] Resolve "Time went backwards" problem by using jiffies as clocksource
From: Daniel Lam <daniel@xxxxxxxxxxxxxxxx>
Date: Mon, 4 Jan 2010 03:44:34 +1100
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Hi All - so I guess nobody has the answers to these questions?
Is there somewhere I can ask, perhaps the developers list?


---------- Forwarded message ----------
From: Daniel Lam <daniel@xxxxxxxxxxxxxxxx>
To: 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 "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?



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