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From: Andreas Kinzler <hfp@posteo.de>
To: xen-devel@lists.xenproject.org, Paul Durrant <Paul.Durrant@citrix.com>
Subject: [Xen-devel] wall clock drift on C24x mainboard, best practices
Date: Sat, 12 Oct 2019 20:47:19 +0200
Message-ID: <4bc44777-103b-ada5-839a-809da33ba00c@posteo.de> (raw)

Hello all, hello Paul,

On a certain new mainboard with chipset C242 and Intel Xeon E-2136 I 
notice a severe clock drift. This is from dom0:

# uptime
  20:13:52 up 81 days,  1:41,  1 user,  load average: 0.00, 0.00, 0.00
# hwclock
2019-10-12 20:27:37.204966+02:00
# date
Sat Oct 12 20:07:19 CEST 2019

Kernel is 4.13.16 vanilla, Xen 4.10.2

So after 81 days uptime there is a difference of over 20 minutes between 
"date" and "hwclock". I operate many Xen servers and have never seen 
such a great drift except on this type of mainboard. What could be the 
reason?

In general, what is the current best practice for NTP sync? Run it in 
dom0? In domU? Both? How does the domU type (Linux HVM/PVM/PVH or 
Windows HVM with WinPV drivers) make a difference?

Regards Andreas

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