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[Xen-devel] Re: [PATCH 1/5] Add a global synchronization point for pvclo

To: Avi Kivity <avi@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 1/5] Add a global synchronization point for pvclock
From: Glauber Costa <glommer@xxxxxxxxxx>
Date: Tue, 26 Oct 2010 08:49:22 -0200
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Zachary Amsden <zamsden@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Tue, 2010-10-26 at 10:14 +0200, Avi Kivity wrote:
> On 10/26/2010 01:30 AM, Jeremy Fitzhardinge wrote:
> > Unfortunately this is breaking Xen save/restore: if you restore on a
> > host which was booted more recently than the save host, causing the
> > system time to be smaller.  The effect is that the domain's time leaps
> > forward to a fixed point, and stays there until the host catches up to
> > the source host...
> 
> Shouldn't save/restore also save the timebase?
> 
> > I guess last_time needs to be reset on this type of event.  I guess the
> > cleanest way would be for pvclock.c to register a sysdev suspend/resume
> > handler.
> 
> Should be for Xen only; kvm save/restore doesn't involve the guest.

the suspend/resume path do adjust the time base. Maybe something similar
should be done ?



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