When observation of the stats_log or state files identifies that the system clock has any of the following symptoms:
- Periodic spikes in offset value.
- Offset value constantly much greater than ~100 ns from the LRC.
- Offset value behaving erratically.
- The in-sync flag value is never 1.
It is possible that the system clock is being adjusted, probed or otherwise being interfered with by a process other than sfptpd.
Another known cause of this is an unstable TSC clock and this will be reported in the kernel logs.