Re: [PATCH v2 1/2] keep guest wallclock in sync with host clock
From: Marcelo Tosatti
Date: Tue Sep 08 2009 - 16:01:36 EST
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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