On Wed, Nov 16, 2011 at 11:06:27AM -0800, Bill Unruh wrote: > On Wed, 16 Nov 2011, Miroslav Lichvar wrote: > >Polling interval was fixed to 64 seconds, the number of samples is > >around 30-40. With higher jitter or more stable clock (longer Allan > > So that is about 1800 sec. which looks to be something like that period > > I suppose not surprizingly, since the linear least squares fitting would > eliminate > any higher frequencies.
I think there is not much chrony can do here to eliminate higher frequencies besides using a shorter polling interval and increasing the maximum number of samples. > What is interesting is that I do not see it in the other runs, which might > suggest that there is something a bit strange in the filtering which is taking > place. I guess you could run the simulations with the jitter zero, and then > the frequency wander zero to see if if one of those were driving it. With this wander/jitter ratio the jitter is the one driving it. Here are another simulations, jitter with wander, only jitter and only wander. http://mlichvar.fedorapeople.org/tmp/chrony_corr4.png http://mlichvar.fedorapeople.org/tmp/chrony_corr4_nowander.png http://mlichvar.fedorapeople.org/tmp/chrony_corr4_nojitter.png With no wander the buffer is mostly full - 64 samples (except the spike in the middle where the number of samples is 8), with no jitter the buffer has mostly fewer than 10 samples. > What do you do, every second add a small random amount to the frequency and a > random amount to the offset with a roughly gaussian distribution? Yes, but only to the frequency. The offset is updated by the difference of the clock and kernel frequency. -- Miroslav Lichvar --- To unsubscribe email chrony-dev-requ...@chrony.tuxfamily.org with "unsubscribe" in the subject. For help email chrony-dev-requ...@chrony.tuxfamily.org with "help" in the subject. Trouble? Email listmas...@chrony.tuxfamily.org.