Re: [Ntp] [EXT] virtual server for ntp server

"Windl, Ulrich" <> Wed, 27 March 2024 07:44 UTC

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From: "Windl, Ulrich" <>
To: Renzo Marengo <>, "" <>
Thread-Topic: [EXT] [Ntp] virtual server for ntp server
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Date: Wed, 27 Mar 2024 07:44:34 +0000
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Subject: Re: [Ntp] [EXT] virtual server for ntp server
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Interestingly „Network Time Protocol Best Current Practices“ does not make a statement about that, but if you think logically:

Assume you have one CPU core and two virtual machine wanting to read the time in a busy loop; how smooth are you expecting the time to be?

Then make another experiment: Read the CPU’s cycle counter and compare it to “wall time”; would you see a constant rate (CPU cycles compared to elapsed wall time)?

So if you don’t over-commit a physical CPU, it might work well enough, but dedicated hardware will run with better statistics, I guess.

The comparison isn’t quite fair, but here are some Offset statistics:

First an old off-the-shelf PC located in a non temperature-controlled room having an even older DCF-77 reference clock (startum-1).

Next an old physical host that is a general-purpose server that also runs NTP (stratum-2).

Finally a virtual server (VMware) that runs as stratum-3.

The last two are housed in a temperature-controlled machine room.

All three are running basically the same operating system (SLES12) and NTP version.

Kind regards,


From: ntp <> On Behalf Of Renzo Marengo
Sent: Friday, March 15, 2024 11:04 AM
Subject: [EXT] [Ntp] virtual server for ntp server

I'm not able to find official document which suggests to not implement ntp server using virtual machine; I'd like to know reasons but specially what RFC shows this recommendation.