[ntp:questions] Tighter regulation?

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Sat May 25 10:14:39 UTC 2013



Edward T. Mischanko | Maintenance Technician, Electrical
ArcelorMittal Burns Harbor
 
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> -----Original Message-----
> From: questions-bounces+edward.mischanko=arcelormittal.com at lists.ntp.org
> [mailto:questions-
> bounces+edward.mischanko=arcelormittal.com at lists.ntp.org] On Behalf Of
> unruh
> Sent: Friday, May 24, 2013 9:55 AM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] Tighter regulation?
> 
> On 2013-05-24, Mischanko, Edward T <Edward.Mischanko at arcelormittal.com>
> wrote:
> >
> >
> >>
> >>
> >> > On 2013-05-21, Mischanko, Edward T
> <Edward.Mischanko at 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
> >>
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