Edward T. Mischanko | Maintenance Technician, Electrical ArcelorMittal Burns Harbor Finishing | 250 W. US Highway 12 Burns Harbor, IN 46304-9745 T +1 219 787 3601 | F +1 219 787 4510 www.arcelormittal.com
> -----Original Message----- > From: questions-bounces+edward.mischanko=arcelormittal....@lists.ntp.org > [mailto:questions- > bounces+edward.mischanko=arcelormittal....@lists.ntp.org] On Behalf Of > unruh > Sent: Friday, May 24, 2013 9:55 AM > To: questions@lists.ntp.org > Subject: Re: [ntp:questions] Tighter regulation? > > On 2013-05-24, Mischanko, Edward T <edward.mischa...@arcelormittal.com> > wrote: > > > > > >> > >> > >> > On 2013-05-21, Mischanko, Edward T > <edward.mischa...@arcelormittal.com> > >> wrote: > >> > > >> >> My concern is that too much data is being thrown away when polling > >> >> above 256 seconds and that allows excessive wandering of my clock. > >> > > >> > >> If too much data is being thrown away, it would be because the poll > >> adjust algorithm has chosen too high a poll interval (or you have too > >> high a minpoll) for the noise statistics. > > [Mischanko, Edward T] > > > > This is exactly what I am saying!! This needs to be corrected; I > consider it a bug. > [Mischanko, Edward T] Are you one of the authors or is this just more unneeded information? > And until you take over the running of ntp, it will remain your opinion, > and not that of the supporter. > > > > > > The samples are, effectively, > >> put through an IIR digital low pass filter, with a bandwidth that is > >> sufficiently narrow that variations across the 8 samples are largely > >> suppressed. However, if you include all the samples, their overall > >> average is likely to be biased away from a zero error, and as that is > >> likely to not change, or only change slowly from one group of 8 to the > >> next, it will introduce an error that is not filtered out. > >> > >> It is not throwing out anything like the equivalent of 7 out of eight > >> samples, because the contributions of the variations between samples > are > >> high frequency noise, which is probably being attenuated by a factor > >> significantly more than 8. > >> > >> The way that ntpd chooses the poll interval is by looking at the offset > >> and jitter (exponential average of sample to sample variations). If > the > >> offset consistently exceeds the jitter, it means that part of the > offset > >> cannot be accounted for by the measurement noise, and more aggressive > >> correction is needed. Unfortunately, if something make the crystal > >> frequency change suddenly, after a long stable period, it can take some > >> time before it realizes it needs to do aggressive correction. > > [Mischanko, Edward T] > > > > It takes too long to figure out it needs a more aggressive correction. > > If I leave maxpoll at the default of 1024 seconds, my clock drifts > outside > > of 5 milliseconds consistently. > [Mischanko, Edward T] To lower maxpoll is to defeat the software author's intent. > So lower maxpoll! > > > > > > Too much assumption is made that everyone will have the perfect computer > and > > the perfect network when configuring these various filters. What works > on > > the blackboard does not always work in reality. My computer has a > > -19 precision but it can't keep time inside 1 millisecond with default > > Settings; go figure. > [Mischanko, Edward T] Yes, maybe unfair, but equally unfair is the assumption that the user must be doing something wrong for it to work this way. I need to be as constructive as possible, as does everyone on this list. I don't know if Dr. Mills is much involved with the Windows port? As for chrony, I would try it if they had a Windows port. > That is unfair. Mills has spent a lot of time making sure it works in > the real world. That his priorities are not yours is surely something he > is entitled to. Why do you not use chrony? I know you have tried it. > > > > > > Regards, > > Ed > >> > >> _______________________________________________ > >> questions mailing list > >> questions@lists.ntp.org > >> http://lists.ntp.org/listinfo/questions > > _______________________________________________ > questions mailing list > questions@lists.ntp.org > http://lists.ntp.org/listinfo/questions _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
