[ntp:questions] Any chance of getting bugs 2164 and 1577 moving?

Alby VA albyva at empire.org
Thu Mar 22 01:03:45 UTC 2012


On Mar 21, 8:16 pm, David Lord <sn... at lordynet.org> wrote:
> Alby VA wrote:
> > On Mar 21, 7:36 pm, unruh <un... at invalid.ca> wrote:
> >> On 2012-03-21, Alby VA <alb... at empire.org> wrote:
>
> >>> On Mar 21, 3:55?pm, unruh <un... at invalid.ca> wrote:
> >>>> On 2012-03-21, David J Taylor <david-tay... at blueyonder.co.uk.invalid> wrote:
> >>>>> "unruh" <un... at invalid.ca> wrote in message
> >>>>>news:itmar.5841$yD7.508 at newsfe15.iad...
> >>>>> []
> >>>>>> But -19 is about 2 microseconds if I understand it correctly. That means
> >>>>>> that the clocks are incapable of delivering more than about 2
> >>>>>> microseconds of accuracy. What is you ?that last decimal digit of
> >>>>>> accuracy in the offset is thus pure noise-- dominated by clock reading
> >>>>>> noise. Why is it important for you then?
> >>>>> When I can see the decimal places, then I will know whether the precision
> >>>>> estimate is reasonable. ?Just getting values such as -1, 0, 1 microseconds
> >>>>> is insufficient to make that call.
> >>>> And how will the extra decimals help? The -19 was determined by making
> >>>> successive calls to the clock and seeing how much it changed between
> >>>> successive readings. That gives a good estimate of how long it takes to
> >>>> make a call to the clock. Any precision in the answer beyond that is not
> >>>> accuracy. I could give you the time to 60000 decimal places, each one of
> >>>> the diffetent, but the last 5995 just being garbage (random numbers)
> >>>> Would that tell yo uanything?
> >>>> If for some reason you do not believe ntpd's estimation of your clock
> >>>> accuracy, develope a better algorithm for determining it. It is a bug is
> >>>> ntpd is reporting an accuracy much worse than it actually is.
> >>>> Ie, you have no data to make that call even if you get more digits.
> >>>>> David
> >>> unruh:
> >>>   My take is the precision output might say your device is -19 so you
> >>> know its
> >>> accuracy is around 2/microseconds. But the offset several decimal
> >>> places
> >>> allows you to see its ever changing accuracy within that 2/microsecond
> >>> band
> >> But that is not accuracy. That is presumably (if that -19 is accurate
> >> and not a bug) is simply noise. If your measurement technique is only
> >> good to 2us, then any additional precision is just noise. It may be fun
> >> to see the noise, but not terribly useful. If it is not noise, then that
> >> -19 is wrong, and one has a bug in the determination of the accuracy of
> >> the clock reading.
>
> >>> to a greater detail than just -1, 0, or 1 microseconds. I guess its
> >>> just a matter
> >>> of getting more granular details for cool MRTG charting. :)
> >> It could well be that charting looks better without just bands on the
> >> page. But is it worth it if that detail is just junk? It certainly is
> >> not great art.
>
> >  It there any good way to determine what is noise and what isn't?
>
> ntpq -c rv gives output including precision= , which on
> my server indicates precision=-19 which is 1/(2^19) or
> approx = 2us
>
> David



 Yup. I'm getting the same thing, precision = -19
In the math, I get 0.0000019073486328125 (1.907/microseconds).

 To improve this to better precision, would the only path of success
be
in getting a better stratum 0 device?


assID=0 status=0415 leap_none, sync_uhf_clock, 1 event,
event_clock_reset,
version="ntpd 4.2.6p5 at 1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)",
processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1,
precision=-19, rootdelay=0.000, rootdisp=0.297, refid=PPS,
reftime=d314f812.ee1ec4ca  Wed, Mar 21 2012 21:00:02.930,
clock=d314f817.b13ef313  Wed, Mar 21 2012 21:00:07.692, peer=21829,
tc=4, mintc=3, offset=0.002, frequency=-24.569, sys_jitter=0.002,
clk_jitter=0.002, clk_wander=0.001




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