In article <qj10eu$1q1r$1...@gioia.aioe.org> Miroslav Lichvar <mlich...@redhat.com> writes: >On 2019-08-14, Per Hedeland <p...@hedeland.org> wrote: >> Anyway, back to the FreeBSD post, it seems there are actually two >> questions: >> >> 1) Is the ~ 200 usec offset reported by ntpd really semi-constant (and >> thus "easy to deal with")? > >My understanding is that the error in the measurement is moving in an >interval at a speed which depends on a hidden frequency offset. ntpd >uses a median from multiple samples for controlling the clock. If the >frequency offset is large enough and the polling interval long enough, >the median should be stable and close to the middle of the interval.
Hm, I guess that could be an alternate explanation (FWIW, the ntpd poll interval was clamped to 16 s via minpoll=maxpoll=4), but... - The test used one USB 1.1 and one USB 2.0 adapter, which should supposedly poll at nominally 1 kHz and 4 kHz, respectively. I.e. "middle of the interval" ought to be 500 usec and 125 usec, respectively, plus some "really constant" offset, while ntpd reported close to 200 usec for both. And, I would expect such a drifting offset to be reflected in a higher jitter. --Per _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
