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

Glauber Costa
2009-09-08T19:37:54Z

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@redhat.com>
>
> 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?