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

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Message-ID: <20090908193752.GH9013@mothafucka.localdomain>
Date:	Tue, 8 Sep 2009 16:37:52 -0300
From:	Glauber Costa <glommer@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH v2 1/2] keep guest wallclock in sync with host clock

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@...hat.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?

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