ntpd Frequency (drift) Jumps - NTP

This is a discussion on ntpd Frequency (drift) Jumps - NTP ; I just started using ntpd. It seems to be most accurate in terms of the offset remaining in the range [-10, 10] ms when the frequency drift is -41.xxx. However, every now and then, for no apparent reason, the frequency ...

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Thread: ntpd Frequency (drift) Jumps

  1. ntpd Frequency (drift) Jumps

    I just started using ntpd. It seems to be most accurate in terms of the
    offset remaining in the range [-10, 10] ms when the frequency drift
    is -41.xxx. However, every now and then, for no apparent reason, the
    frequency will jump +- 50 to 100 PPM. When it does, the offset increases
    greatly in magnitude, becomes wildly erratic, and ntpd adjustes the clock
    frequently. In a day or so ntpd will slowly reduce the drift to -4y.xxx,
    then
    it will start the cycle again. I am using ntpd 4.2.0b from
    ntp-4.2.0b@1.1436mbg-xmas-o-win32-setup.exe. Has anyone else
    noticed this behavior? Do you know of a remedy?

    C Elliott



  2. Re: ntpd Frequency (drift) Jumps

    Charles Elliott wrote:
    > I just started using ntpd. It seems to be most accurate in terms of
    > the offset remaining in the range [-10, 10] ms when the frequency
    > drift is -41.xxx. However, every now and then, for no apparent reason,
    > the
    > frequency will jump +- 50 to 100 PPM. When it does, the offset
    > increases greatly in magnitude, becomes wildly erratic, and ntpd
    > adjustes the clock frequently. In a day or so ntpd will slowly
    > reduce the drift to -4y.xxx, then
    > it will start the cycle again. I am using ntpd 4.2.0b from
    > ntp-4.2.0b@1.1436mbg-xmas-o-win32-setup.exe. Has anyone else
    > noticed this behavior? Do you know of a remedy?
    >
    > C Elliott


    Do you have the Multi-Media timer option set? It was critical to getting
    good stability with my systems:

    http://www.david-taylor.myby.co.uk/n...nts.htm#glitch

    David



  3. Re: ntpd Frequency (drift) Jumps

    Yes, the Multi-Media timer option (-M) is set.

    CHE

    "David J Taylor"
    wrote in message news:9uNpg.94762$wl.82500@text.news.blueyonder.co. uk...
    > Charles Elliott wrote:
    >> I just started using ntpd. It seems to be most accurate in terms of
    >> the offset remaining in the range [-10, 10] ms when the frequency
    >> drift is -41.xxx. However, every now and then, for no apparent reason,
    >> the
    >> frequency will jump +- 50 to 100 PPM. When it does, the offset
    >> increases greatly in magnitude, becomes wildly erratic, and ntpd
    >> adjustes the clock frequently. In a day or so ntpd will slowly
    >> reduce the drift to -4y.xxx, then
    >> it will start the cycle again. I am using ntpd 4.2.0b from
    >> ntp-4.2.0b@1.1436mbg-xmas-o-win32-setup.exe. Has anyone else
    >> noticed this behavior? Do you know of a remedy?
    >>
    >> C Elliott

    >
    > Do you have the Multi-Media timer option set? It was critical to getting
    > good stability with my systems:
    >
    > http://www.david-taylor.myby.co.uk/n...nts.htm#glitch
    >
    > David
    >




  4. Re: ntpd Frequency (drift) Jumps

    Charles Elliott wrote:
    > Yes, the Multi-Media timer option (-M) is set.
    >
    > CHE


    Well, that leaves drivers taking too much time time at interrupt level
    (PIO mode on the disks), or something else. It could be bad hardware on
    your motherboard. Do you have any spread-spectrum or power-saving
    functions set in your BIOS?

    Cheers,
    David



  5. Re: ntpd Frequency (drift) Jumps

    No, this motherboard does not seem to have any spread-spectrum functions; I
    looked thru the BIOS
    setup screen and in the manual. AFIK power-saving is disabled. I do run
    Seti@Home on both CPUs, which can make the system seem sluggish at times.
    Also hyperthreading is enabled so
    it appears as 2 CPUs. I was looking thru the ntpd code and in at least one
    place they claim to
    have made a fix that will work on single processor systems, but might not
    work on multiprocessor
    systems. I am considering moving it over to a Server 2003 single-cpu AMD 64
    machine to see if
    the same problem appears.

    The problem always seems to happen when the time offset is very small (< 5
    ms) and is about to change sign. I wrote a Java routine to call ntpq every
    5 seconds and I have been watching it for the last half hour. The offset
    just did change from -0.979 ms to 2.711 ms with no untoward result.

    It always happens late in the evening or in the very early morning. Verizon
    is making changes to its DSL system, and so there have been some outages and
    slow downs at these times. Also the 50 to 100 and one 500 PPM frequency
    jumps are always accompanid by a large time adjustment (on the order of .180
    seconds).

    Do you have any more ideas?

    CHE

    "David J Taylor"
    wrote in message news:tROpg.94815$wl.28713@text.news.blueyonder.co. uk...
    > Charles Elliott wrote:
    >> Yes, the Multi-Media timer option (-M) is set.
    >>
    >> CHE

    >
    > Well, that leaves drivers taking too much time time at interrupt level
    > (PIO mode on the disks), or something else. It could be bad hardware on
    > your motherboard. Do you have any spread-spectrum or power-saving
    > functions set in your BIOS?
    >
    > Cheers,
    > David
    >




  6. Re: ntpd Frequency (drift) Jumps

    Charles Elliott wrote:
    []
    > Do you have any more ideas?
    >
    > CHE


    Sorry, I don't. My own measurements with Windows are on a +/- 100ms
    timescale rather than anything finer, and I now have a simple stratum 1
    source rather than relying purely on Internet sources.

    Cheers,
    David



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