Re: [Xen-devel] wall clock drift on Coffee Lake / C24x mainboard (HPET broken?), best practices

[Andreas Kinzler <hfp@xxxxxxxxx>]

Hello All,

I came across the following: https://lkml.org/lkml/2019/8/29/536

Could that be the reason for the problem mentioned below? Xen is using 
HPET as clocksource on the platform/mainboard. Is there an (easy) way to 
verify if Xen uses PC10?
Regards Andreas

On 12.10.2019 20:47, Andreas Kinzler wrote:
> 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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