Re: Measuring clock offset results
Bill Unruh <[email protected]>
| Newsgroups | gmane.comp.time.chrony.user |
|---|---|
| Message-ID | <[email protected]> |
On Wed, 19 Jul 2023, Miroslav Lichvar wrote: > [CAUTION: Non-UBC Email] > > On Wed, Jul 12, 2023 at 09:52:11AM -0700, Thangalin wrote: >> https://ibb.co/album/1Z824p >> >> Are there any other ways we could help chronyd stay below 20 microseconds >> (e.g., optimized build) that may have been overlooked (besides using GPIO)? > > If you zoom on those spikes and see that they are just single > samples, it's probably not an error of the clock, but rather a > measurement error (e.g. due to interrupt delays). You should implement > some filtering in your program, e.g. use the median value from a > number of consecutive samples (e.g. 5). That's what both ntpd and > chronyd are doing with the data they get. Also you could eliminate one or 2 data points which are way off (say 2 standard deviations or two deviations ( Sum_i (|t_i-t_median|)/N) from the median. Such events Mills calls popcorn events-- they are not gaussian distributed and are probably caused by single transient events (eg like interrupt delays, or path delays (eg the routing algorithm suddenly sends a packet from NY to Washington via Beijing for some unknown reason)). So getting rid of such popcorn events can improve the signals a lot. > > -- > Miroslav Lichvar > > > -- > To unsubscribe email chrony-users-request-kWFZVVI9zxvPqho9SqqRMmD2FQJk+8+b@public.gmane.org > with "unsubscribe" in the subject. > For help email chrony-users-request-kWFZVVI9zxvPqho9SqqRMmD2FQJk+8+b@public.gmane.org > with "help" in the subject. > Trouble? Email [email protected] > > -- To unsubscribe email chrony-users-request-kWFZVVI9zxvPqho9SqqRMmD2FQJk+8+b@public.gmane.org with "unsubscribe" in the subject. For help email chrony-users-request-kWFZVVI9zxvPqho9SqqRMmD2FQJk+8+b@public.gmane.org with "help" in the subject. Trouble? Email [email protected]