From: Paolo Bonzini <pbonzini@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
David Matlack <dmatlack@google.com>,
Peter Hornyack <peterhornyack@google.com>,
KVM list <kvm@vger.kernel.org>
Subject: Re: TSC deadline timer in guests vs. migration?
Date: Mon, 4 Jul 2016 16:17:55 -0400 (EDT) [thread overview]
Message-ID: <1372974489.3861514.1467663475048.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <20160704194506.GE4131@thinpad.lan.raisama.net>
> 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?
Indeed. We need a way to compute the deadline that is customized
for kvmclock, and uses the kvmclock page instead of tsc_khz.
Paolo
next prev parent reply other threads:[~2016-07-04 20:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-04 11:01 TSC deadline timer in guests vs. migration? Paolo Bonzini
2016-07-04 19:07 ` Eduardo Habkost
2016-07-05 10:48 ` Paolo Bonzini
2016-07-04 19:30 ` Marcelo Tosatti
2016-07-04 19:45 ` Eduardo Habkost
2016-07-04 20:17 ` Paolo Bonzini [this message]
2016-07-05 12:51 ` Marcelo Tosatti
2016-07-05 13:04 ` Eduardo Habkost
2016-07-05 13:34 ` Paolo Bonzini
2016-07-05 18:11 ` Eduardo Habkost
2016-07-05 21:40 ` Paolo Bonzini
2016-07-05 22:12 ` Eduardo Habkost
2016-07-06 6:01 ` Paolo Bonzini
2016-07-05 20:39 ` Marcelo Tosatti
2016-07-05 21:41 ` Paolo Bonzini
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