[time-nuts] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is "Good Enough"?

Chris Caudle chris at chriscaudle.org
Mon Jun 15 21:38:39 EDT 2015

On Mon, June 15, 2015 8:01 pm, Bob Camp wrote:
> Unless you have fancy switches on your LAN (1588 stamping), PTP
> performance will be dependent on load and the "goodness" of the switches
you do
> have. These are pretty much the same (external)  things that impact NTP.

Yes, but proper differentiated services setup with multiple queues can
help mitigate that to a large extent.  I'm still trying to get my PTP
setup going, so I don't have any measurements of my own yet, but there are
lots of examples of large commercial systems in use without transparent
clock support which can maintain sub-microsecond synchronization.  Using
PTP transparent switches should get down into the couple hundred
nanosecond range or better, but even without 800 or so nanoseconds has
been shown to be consistently possible.
I have no idea what level of synchronization you could keep using just NTP
with diffserv.  That might be an interesting experiment to try for those
who only want NTP and aren't interested in setting up PTP.

Chris Caudle

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