Re: [Xen-users] Time/clock issues with Xen 3.0.3?

[Tim Post <tim.post@xxxxxxxxxxxxxxx>]

On Fri, 2006-11-24 at 20:28 +0000, Phillip Mumford wrote:
> The time appears to be perfect inside dom0, however all the domU's
> tend to have a slightly faster date which gets further out of sync
> every day.
> 
> I'm currently using Xen 3.0.3 with Gentoo Linux, under 3.0.2 I had no
> problems with domU clocks.  Are there any known issues which could
> cause this?   I'd strongly prefer not to run ntpd in every domU,
> having all domU clocks in sync with dom0 is quite important for me.
> 

What are the values of /proc/sys/xen/independent_wallclock
and /proc/sys/xen/permitted_clock_jitter respectively?

By default, your guests should be using dom-0's clock and should always
be in sync. I have found that when I use independent HW clocks that the
guests tend to stay a little behind dom-0, but I always chalked this up
to a second or so difference between whatever ntp server the guests were
using vs dom-0

Since the only reason to keep them independent is to allow for a
difference, I never gave it much thought :)

If you do a head -c1 /dev/null > /proc/sys/xen/independent_wallclock (or
echo 0 to it) then rdate on dom-0, your guests should have the exact
time as dom-0.

I'm also not sure of what unit is used in permitted_clock_jitter in
order to guide you on changing it .. can't seem to find that one in the
docs. If you found independent wall clocks to already be null or 0, you
might try adjusting the permitted jitter.

Hope this helps.

Best,
- Tim

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