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Re: [Xen-devel] [Bug 1759] Xen 4.0.1 live migration/restore over-writes

To: Keir Fraser <keir.xen@xxxxxxxxx>
Subject: Re: [Xen-devel] [Bug 1759] Xen 4.0.1 live migration/restore over-writes new hypervisor's boot-time record
From: Tim M <bugs@xxxxxxxxxxxxxx>
Date: Wed, 13 Apr 2011 12:31:57 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
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On Wed, Apr 13, 2011 at 07:34:01PM +0100, Keir Fraser wrote:
> The fix is still there, albeit in a modified form since the restore code has
> changed quite a bit since Xen 3. Can you reliably repro this, with any PV
> guest?
>  -- Keir

This is 100% reproducible. Every time I migrate from a host with an uptime
longer than the target host, the VM has a clock/time freeze for however long
the uptime difference is. Migrating from a host with shorter uptime to a host
with longer has no problem.

As a demonstration, I have two dom0 hosts that have roughly 6 minutes
difference in uptime. I started a guest VM on the dom0 host with a longer
uptime then SSH'd to the guest and ran this command:

while true ; do date ; sleep 5 ; done

Next I initiated a live migration and this is what the output of the command
looks like (with commentary added):

Wed Apr 13 12:07:48 PDT 2011
Wed Apr 13 12:07:53 PDT 2011
Wed Apr 13 12:07:58 PDT 2011
Wed Apr 13 12:08:03 PDT 2011  [ migration happens here and SSH to the guest 
"freezes" for about 6 min ]
Wed Apr 13 12:13:55 PDT 2011
Wed Apr 13 12:14:00 PDT 2011
Wed Apr 13 12:14:05 PDT 2011

I have only tried Ubuntu 10.04.2 guests running the 2.6.32 and 2.6.35 server
kernel packages but, as mentioned, this happens every time.

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