The problem with ntpd is the sudden performance degradations which can occur when conditions deviate from ‘ideal’. We have detailed these robustness issues of ntpd in prior work, including [17, 18]. Simply put, when path delay variability exceeds some threshold, which is a complex function of parameters, stability of the feedback control is lost, resulting in errors which can be large over small to very long periods. Recovery from such periods is also subject to long convergence times […]
Now to the results. As expected, and from the very
first migration, ntpd exhibits extremely large errors (from
-1 to 27 s!) for periods exceeding 15 minutes (see zoom
in middle plot) and needs at least another hour to converge
to a reasonable error level.
from Virtualize Everything but Time, Broomhead ,Cremean,Ridoux,Veitch
TimeKeeper is a “from ground up” implementation of clock synchronization over both PTP and NTP and does not share NTPd limits.