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Date: Fri, 6 Jan 2017 11:18:46 +0000
From: 'Roger Pau =?iso-8859-1?Q?Monn=E9'?= <roger.pau@citrix.com>
To: Jay West <jwest@ezwind.net>
CC: "'Hoyer-Reuther, Christian'" <Christian.Hoyer-Reuther@cac-chem.de>,
 <freebsd-xen@freebsd.org>, <owner-freebsd-xen@freebsd.org>
Subject: Re: 11-RELEASE and live migration
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On Thu, Jan 05, 2017 at 03:52:13PM -0600, Jay West wrote:
> 
> Roger wrote...
> > I'm able to see these glitches, as said the VM doesn't really hang, it 
> > just gets stuck for a long time (and I think that depends on the 
> > uptime differences between the source and destination hosts). In the 
> > meantime, could you please test if changing the timecounter from 
> > XENTIMER to any other (like HPET or
> > ACPI-fast) solves the issue?
> > 
> > # sysctl -w kern.timecounter.hardware=ACPI-fast
> 
> Christian replied...
> I changed the timecounter from XENTIMER to ACPI-fast and then I did about 10
> migrations between our 3 hosts. I always started the next migration a few
> seconds after the previous migration finished. The VM didn't stuck now and I
> didn't see the VGABios screen on the console.
> 
> I can also add to this... changing timecounter to ACPI-fast definitely fixes
> the problem. I can migrate a handful of freebsd11 vm's back and forth and
> all stay running correctly.
> 
> So... bug in XENTIMER?

Not exactly, let's say it's a shortcoming of the current resume procedure. IF
you want to know more about the gory details:

https://lists.freebsd.org/pipermail/freebsd-arch/2016-December/018041.html

I'm currently quite busy, so I don't really have an ETA of when this is going
to be fixed.

Roger.