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[Xen-devel] Re: [PATCH] [Bugfix][pv-ops] Guest get stucked after migrati

To: xen-devel@xxxxxxxxxxxxxxxxxxx, Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] [Bugfix][pv-ops] Guest get stucked after migration
From: Frank Pan <frankpzh@xxxxxxxxx>
Date: Tue, 22 Mar 2011 12:19:53 +0800
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On Tue, Mar 22, 2011 at 2:26 AM, Frank Pan <frankpzh@xxxxxxxxx> wrote:
> In recent pv-ops kernel, pvclock is not guaranteed as monotone.
> After a migration, pvclock can produce smaller cycle count.
> [The test is performed on next-2.6.32 tree]
> The issue occured when uptime(sender) > uptime(target), and with
> CONFIG_GENERIC_TIME. The guest get stucked after the migration,
> doing a huge loop inside update_wall_time, until the overflow of
> 64-bit unsigned offset.
> The following patch fixed this issue by introducing a global sign.
> Xen pvclock will update the cycle_last with the newest cycle count
> on the first read after migration.

It seems the issue is not that simple. This issue can be well solved by
the suspend/resume code of timekeeper sysdev. However, the recent
code may think this is not necessary on hvm domain. (How can I find the
reason here?)

I don't know if it's ok to add a pair of sysdev_suspend/sysdev_resume inside
xen_hvm_suspend. If not, this patch can be a quickfix/solution.

Any ideas on this issue?

潘震皓, Frank Pan

Computer Science and Technology
Tsinghua University

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