[ntp:questions] ntp too aggressive on clock changes
Mischanko, Edward T
Edward.Mischanko at arcelormittal.com
Sat Apr 13 20:51:29 UTC 2013
Unless ntp is over shooting in its corrections, you don't have a problem with ntp, per say. NTP is configured to slew all corrections less than 0.128 seconds. If after a day to settle down, you still have big jumps, then, you definitely have a clock problem.
> I am running Ubuntu 12.04 LTS, running v4.2.6 ntp, but I am finding that
> ntp is too agressive on clock changes. The loopstats show clock changes
> up to 0.11+ secs which is way too high. I just set the ntp.conf parameter
> "slewalways" to "yes", hoping that the maximum clock adjustment will be in
> the neighborhood of 0.5 msec.
> In the meantime, I am trying to replace the std CMOS clock with a +/- 2ppm
> precision oscillator so I don't have big startup time deltas (I have seen
> 2 secs at times). Yes, I know a precision pps board using a GPS
> disciplined clock is the best way to go here, but I have to make due with
> an accurate RTC and ntp.
> Are there any other things I need to set, so ntp won't adjust the sys
> clock with steps greater than 0.5 msec ? I run a program during the day
> which does hundreds of thousands of time stamps, and found that it had
> glitches due to clock changes being more than it could tolerate.
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