Re: [Xen-devel] time drift on dom0

[maney@xxxxxxxxx (Martin Maney)]

On Sat, Jan 15, 2005 at 05:31:34PM -0600, Adam Heath wrote:
> On Sat, 15 Jan 2005, Adam Heath wrote:
> > I have just noticed a 9s drift in 12 hours in dom0(not running ntp, hadn't 
> > yet
> > been installed).

> But if each instance(dom0 included) must run ntp, then that is more of a
> problem.
> 
> Is it possible to link the times of the instances?

UML does something along these lines - the guests (domX: x > 1) get
their timing from the host (dom0).  But that works because the guest
kernel there is running as a user process in the host environment.  Xen
would need to invoke interdomain messaging to pass queries, which
offhand sounds more costly.

I'm unsure if I replied earlier to the list, so let me point out that
IME drifts up to 200 ppm can be found outside of Xen with contemporary
PC hardware.  That's about the same Adam's reported drift, or 4 minutes
per week.  This would all be more interesting if drift under Xen could
be compared to the same piece of hardware's drift without Xen, holding
all else as much the same as practical.

-- 
This is not the first time databases and file systems have
collided, merged, argued, and split up, and it won't be the last.
The specifics of whether you have a file system or a database
is a rather dull semantic dispute  -- Rob Pike



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