Re: [PATCH v2 1/2] keep guest wallclock in sync with host clock

[Marcelo Tosatti]

On Tue, Sep 08, 2009 at 04:37:52PM -0300, Glauber Costa wrote:
> On Tue, Sep 08, 2009 at 03:41:59PM -0300, Marcelo Tosatti wrote:
> > On Wed, Sep 02, 2009 at 10:34:57AM -0400, Glauber Costa wrote:
> > > KVM clock is great to avoid drifting in guest VMs running ontop of kvm.
> > > However, the current mechanism will not propagate changes in wallclock value
> > > upwards. This effectively means that in a large pool of VMs that need accurate timing,
> > > all of them has to run NTP, instead of just the host doing it.
> > > 
> > > Since the host updates information in the shared memory area upon msr writes,
> > > this patch introduces a worker that writes to that msr, and calls do_settimeofday
> > > at fixed intervals, with second resolution. A interval of 0 determines that we
> > > are not interested in this behaviour. A later patch will make this optional at
> > > runtime
> > > 
> > > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
> > 
> > As mentioned before, ntp already does this (and its not that heavy is
> > it?).
> > 
> > For example, if ntp running on the host, it avoids stepping the clock
> > backwards by slow adjustment, while the periodic frequency adjustment on
> > the guest bypasses that.
> 
> Simple question: How do I run ntp in guests without network?

You don't.

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