On Tue, Sep 08, 2009 at 05:00:04PM -0300, Marcelo Tosatti wrote: > 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 <glom...@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? > > You don't. For those guests, the mechanism I am proposing comes handy.
Furthermore, it is not only optional, but disabled by default. And then even if you have a network, but a genuine reason not to use ntp in your VMs, you can use it too. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
