[chrony-users] Possible to get sub-millisecond accuracy?

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Is it possible to get clock accuracy in the microseconds using chrony and a local time server?

I have tried with ntpd and the best I have seen is 5 ms accuracy (according to ntpstat). I have tweaked polling intervals but still the best is 5 ms.

I have a local GPS NTP/PTP time appliance, and on the same switch, a few servers. One of the servers has a Solarflare PTP-enabled network card and we are running sfptpd. On that host, our delay to our appliance varies generally by less that 50 ns, with some jitter into the 150 ns range. In short: little jitter in our network, and only one (local) hop between time server and client.. 

I have another server that I need to discipline using NTP. This is because it's CentOS 6.3, which lacks the facilities to support ptp.(see http://linuxptp.sourceforge.net/, "In July of 2011, the PTP Hardware Clock (PHC) subsystem was merged into Linux version 3.0..."). Upgrading to CentOS 7 is not on option right now, due to work priorities for our development crew.

In short: The business wants microsecond accuracy today and PTP will have to wait on CentOS 7 which will be a couple of weeks down the road due to our development priorities.

-Mike Schwager

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