From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eduardo Habkost <ehabkost@redhat.com>
Subject: Re: TSC deadline timer in guests vs. migration?
Date: Mon, 4 Jul 2016 16:45:06 -0300
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 <20160704193005.GA28201@amt.cnet>
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Cc: Paolo Bonzini <pbonzini@redhat.com>,
	David Matlack <dmatlack@google.com>,
	Peter Hornyack <peterhornyack@google.com>,
	KVM list <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
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On Mon, Jul 04, 2016 at 04:30:08PM -0300, Marcelo Tosatti wrote:
> On Mon, Jul 04, 2016 at 01:01:42PM +0200, Paolo Bonzini wrote:
> > Can bad things happen if a guest using the TSC deadline timer is
> > migrated?  The guest doesn't re-calibrate the TSC after migration, and
> > the TSC frequency can and will change unless your data center is
> > perfectly homogeneous.
> 
> It can fire earlier if the destination runs at a higher frequency.
> It will fire past the configured time if the destination runs at a slower frequency.
> 
> Suppose the first case is worse.
> 
> Should convert the expiration time to nanoseconds i suppose, and then 
> convert back on the destination.

This won't make any difference if the guest sets up a new timer
after migration (but using the old TSC frequency), will it?

-- 
Eduardo