| Re: [chrony-users] Comparing timekeeping performance with chronyd to ntpd |
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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Comparing timekeeping performance with chronyd to ntpd
- From: Watson Ladd <watson@xxxxxxxxxxxxxx>
- Date: Thu, 2 May 2019 10:44:22 -0700
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On Thu, May 2, 2019 at 1:35 AM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
>
> On Tue, Apr 30, 2019 at 10:49:29AM -0700, Watson Ladd wrote:
> > On Tue, Apr 30, 2019 at 5:15 AM MUZZULINI Frank
> > <Frank.MUZZULINI@xxxxxxxxxxxxxx> wrote:
> > >
> > > Well, no daemon can be more precise than its sources.
> > > I would use independent measurements against the same source(s) individually using "ntpdate -q <addr>" and/or "chronyd -Q -f <addr.cfg>" (*). Preferably both.
> >
> > That's our plan, but we're not sure what sort of analysis to do on the
> > results. (We will be using a GPS slaved rasbperry pi to gather the
> > results).
>
> Are you interested in measuring the stability/accuracy of the system
> clock on the machine running ntpd/chronyd, or stability/accuracy of
> the time it provides as an NTP server? That would be two different
> things.
We're interested in the stability and accuracy of the system clock and
of the time provided as an NTP server for the nodes we have serving
time.
>
> A RPI synchronized to PPS for testing an NTP server or client should
> be accurate to about 20 microseconds. If you need more accurate
> measurements, you would need something with hardware timestamping and
> ideally a PPS input on the NIC itself (e.g. I210/I211) rather than a
> serial port.
20 microseconds are fine.
>
> Here are some measurements I did with a RPI and other hardware:
>
> https://fedorapeople.org/~mlichvar/ntpserver/
>
> --
> Miroslav Lichvar
>
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