[ntp:questions] Re: Taming the pinball machine

Roy roy at suespammers.org
Mon Nov 17 04:30:05 UTC 2003


"David L. Mills" wrote in message news:<3FA9CC42.58299EA5 at udel.edu>...
>
> There have been several recent reports that certain configuration
> scenarios experience somewhat naughty behavior when a valid
> synchronization source is found after a holdover during which only the
> local clock driver winds the clock. The result is a nasty frequency
> surge that takes some time to dissipate.

FYI, I've seen a similar frequency surge without having the local
clock driver configured.  Here are example loopstats generated with
the original 4.2.0 release.  This looks like nominal adjustments
between poll intervals 9 and 12:

52946 32623.023 0.004414376 -122.306024 0.030704245 0.029020 9
52946 33647.020 0.003290657 -122.304455 0.029715764 0.025144 10
52946 34161.019 0.007188568 -121.970303 0.028514591 0.168489 10
52946 34672.028 0.011901096 -121.557778 0.025280663 0.252657 10
52946 35696.026 0.011828203 -121.500943 0.022135103 0.220645 10
52946 36721.021 0.012520656 -121.380475 0.019331504 0.200353 11
52946 37744.019 0.014827820 -121.123208 0.016837202 0.215992 11
52946 38767.020 0.011270369 -121.417935 0.014913665 0.238129 11
52946 40815.018 0.012852483 -121.201459 0.013160134 0.232905 12

Between 14 and 16, the frequency adjustments became more pronounced:

52947 3570.023 0.027249104 -120.865829 0.039217946 0.568073 14
52947 19955.025 0.056365251 -119.926354 0.041902504 0.680208 15
52947 36339.022 0.005975020 -120.916182 0.050293743 0.769384 15
52947 52725.027 -0.052044137 -122.093038 0.054006568 0.888938 15
52947 85492.026 0.004573343 -121.005418 0.057051619 0.942543 16
52948 31862.023 0.062506310 -120.119140 0.058408479 0.928796 15
52948 64632.024 -0.048148949 -121.206550 0.076392624 0.970882 15
52949 10999.026 -0.155267736 -122.326981 0.086870017 1.010347 15
52949 43767.024 -0.099776332 -121.858918 0.082285588 0.905744 16

By the time the poll interval climbs to 17, the frequencies and time
offsets are jumping all over the place.

52949 76535.023 -0.042154193 -121.026594 0.078694650 0.887958 16
52950 22905.022 0.013110888 -120.203082 0.076081072 0.872293 17
52951 67581.024 -0.419374902 -124.594881 0.128691301 2.322207 16
52954 70497.039 1.383547201 -120.239999 0.446881767 2.964074 16
52954 70514.031 1.371672806 -124.190652 0.580923284 3.239015 17
52956 28768.040 1.469172093 -122.809917 0.528822809 2.888775 17
52956 28774.108 1.524055147 -86.218412 0.479233267 18.466005 17
52957 73448.113 1.612414477 34.247289 0.429699568 62.319670 16

This was the last loopstat generated, since I stopped ntpd shortly
after this.  I grew tired of watching the pinball machine.  When ntpd
was stopped, the time was nearly 26 seconds off.  I've now restarted
again with the revised algorithms.

> 2. Really DO use burst mode (both iburst and burst keywords) if you
> intend to operate much above the default maximum.

When burst mode is used, that hits the servers with 8 packets each
poll rather than just one.  That doesn't seem to help reduce the
server load much. :{
Hmmm, I wonder which configuration gives better results:
    maxpoll 17 with burst
    maxpoll 14 without burst

Have a great time,
 

roy
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