[ntp:questions] Win7: ntpd adjusting time backwards

Jeroen Mostert jmostert at xs4all.nl
Wed Dec 12 07:35:22 UTC 2012


On 2012-12-12 01:20, David Lord wrote:
> Jeroen Mostert wrote:
>> On 2012-12-11 22:10, E-Mail Sent to this address will be added to the
>> BlackLists wrote:
>>> Jeroen Mostert wrote:
>>>> I noticed the drift was ever-increasing, slowly but surely.
>>>> Since I muddled with settings quite a bit, I stopped ntpd,
>>>> deleted ntp.drift and restarted it.
>>>> The results are quite interesting.
>>>> 56272 68581.536 0.022139147 2.356 0.006080932 0.008049 10
>>>> 56272 68781.535 0.021885071 2.357 0.005698660 0.007537 10
>>>> 56272 69311.535 0.020898356 2.359 0.005342012 0.007109 10
>>>> 56272 71122.534 0.023597293 0.000 0.008392764 0.000000 6
>>>> 56272 71458.536 0.013381279 39.825 0.012521981 0.000000 6
>>>> 56272 71524.551 0.009503058 39.825 0.011793222 0.000000 6
>>>> 56272 71527.552 0.000754424 39.825 0.011456980 0.000000 6
>>>> 56272 71528.552 0.000233147 39.825 0.010722584 0.000000 6
>>>> 56272 71930.577 -0.013119319 39.511 0.011085491 0.111141 6
>>>> 56272 72003.578 -0.016005287 39.441 0.010419607 0.106838 6
>>>> 56272 72207.579 -0.031178859 39.062 0.011125504 0.167193 6
>>>> 56272 72331.588 -0.032740845 38.820 0.010421598 0.178267 6
>>>> 56272 72607.596 -0.036786552 38.215 0.009852891 0.271267 7
>>>> 56272 72611.597 -0.048063956 38.212 0.010042013 0.253749 7
>>>> 56272 72667.599 -0.050119893 38.170 0.009421524 0.237821 7
>>>> 56272 72960.613 -0.050045193 37.952 0.008819790 0.235492 6
>>>> 56272 73291.594 -0.049274393 36.980 0.008257379 0.408236 6
>>>> 56272 73419.587 -0.049355146 36.603 0.007731784 0.404411 6
>>> day, second, offset, drift, est error, stability, poll
>>> comp
>>>
>>> I looked at several of the last few days of loopstats
>>> on a few machines; it appears your drift compensation
>>> change rate is perhaps hundreds of times what mine are?
>>>
>>> I'm not certain what that means, is the PC/Device experiencing
>>> large Temperature Swings, or Cpu/Core Frequency/Power Management?
>>>
>> Improbable. I've admittedly not measured, but the machine has been running
>> constantly for three days in a room with even heating, with no significant
>> change in load. I don't think there's any way temperature could explain this
>> much drift. CPU frequency remains constant and power management has been
>> turned off.
>>
>> I suspect some driver or other is giving me trouble, preventing ntpd from
>> getting decent readings from the clock. Or maybe the machine is just broken
>> (clockwise, I mean), I guess that happens.
>>
>> For kicks, I repeated the procedure -- stop ntpd, delete the drift file, start
>> ntpd, forcing it to do yet another drift calibration. (The servers must love
>> me.) The difference isn't quite so dramatic, but still notable.
>>
>> 56272 76491.581 -0.039118819 30.383 0.004118758 0.429325 6
>> 56272 76748.567 -0.038717153 29.790 0.003868185 0.453044 6
>> 56272 76884.559 -0.035856775 29.500 0.003757023 0.436066 6
>> 56272 76929.557 -0.023728814 29.436 0.005544073 0.408522 6
>> 56272 77378.579 -0.030387567 0.000 0.010782393 0.000000 6
>> 56272 77719.530 0.011532945 33.821 0.031973641 0.000000 6
>> 56272 77719.532 0.012297079 33.821 0.029910596 0.000000 6
>> 56272 77783.546 -0.000656742 33.821 0.028351163 0.000000 6
>> 56272 77800.543 -0.000072661 33.821 0.026522332 0.000000 6
>> 56272 78118.559 0.001651644 33.852 0.024816859 0.011068 6
>> 56272 78127.560 -0.003217920 33.851 0.023277801 0.010371 6
>> 56272 78193.560 -0.007368853 33.822 0.021823790 0.014112 6
>> 56272 78197.561 -0.014632962 33.818 0.020575203 0.013258 6
>> 56272 78257.562 -0.015837880 33.761 0.019251054 0.023555 7
>> 56272 78989.594 -0.023846042 33.501 0.018228934 0.094564 7
>> 56272 79047.605 -0.024689830 33.480 0.017055101 0.088777 7
>>
>> The moral of this story is, uhm... time is not on my side.
>>
>
> Here if ntpd is in sync, stopped, driftfile deleted, ntpd
> restarted the time taken to resync with creation of a new
> driftfile can be anything from a few hours to a few days.
>
I've just observed the same behavior on a server running Windows Server 2012 
which is far better at keeping track of time -- it can take a really, really 
long time before the drift stabilizes.

I've decided to terminate the NTP experiment for my home machine. Normally, it's 
turned off for the night, and in the interest of conserving power I'll return to 
that policy.

Even with the problems ntpd has it's still better than nothing, and as long as 
it can keep the actual offset within one second (a very loose goal it has no 
trouble meeting) it's acceptable. My machine isn't used for anything where 
accurate time is critical, or even useful.

> What's the value of your driftfile?
>
At present, 32.980, but the value is still trending downwards.

-- 
J.



More information about the questions mailing list