Re: [chrony-users] Massive difference between NTP clocks and PHC

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On Fri, 14 Oct 2016, Denys Rtveliashvili wrote:


I have tried adding PHC to the configuration of chrony and see things like

What is PHC? Could it be trailing-vs-leading-edge-of-a-pulse problem?

MS Name/IP address         Stratum Poll Reach LastRx Last sample
#x PHC0                          0   3   377    11 -322ms[ -322ms] +/-    2ns
^* ntp-clock-1 1 4 377 11 -2579ns[-4000ns] +/- 441us ^- ntp-clock-2 1 4 377 11 -2000ns[-2000ns] +/- 31ms

322ms is a huge offset and I wonder if anybody has an idea of what could be the root source.

ntp-clock-1 and ntp-clock-2 are two proper grandmasters.
ntp-clock-2 is geographically far.
ntp-clock-1 is in the same location.

PHC0 is a clock on an Intel card running under igb driver.
The PTP port of the card is connected to a PTP-enabled Cisco Nexus switch, which is connected to a PTP grandmaster. The same grandmaster in fact, which is also a NTP source ntp-clock-1.

I would understand 36 secons of a difference (TIA vs GMT) or some microseconds of a difference (some network and PCIE jitter). But a third of a second is very strange.
Do you have any ideas?

By the way, for synchronization of on-the-NIC PTP clock I tried using ptp4l in both software and hardware mode and that did not make any difference.

With kind regards,
Denys Rtveliashvili


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