[ntp:questions] Should ntpd be run with highest priority (-N)?

Chris Albertson albertson.chris at gmail.com
Wed Sep 14 20:29:41 UTC 2011


On Wed, Sep 14, 2011 at 11:07 AM, Fran <fran.horan at jhuapl.edu> wrote:
> Chris,
>
> That is a good point, I hadn't thought of reference clocks case(s) and
> interrupt level processing which will be at a higher priority than the
> ntpd process. I was thinking all network connections between ntpd
> processes.
>
> That then made me think about later stages of ntpd processing where
> ntpd has decided to adjust the clock some amount. What if pre-emptions
> happen in that segment of processing, where the adjustment value was
> calculated but not actually applied yet ?

So what you say is that NTP calculates the error in the clock at some
point in time.   Then adjusts the clock at some other point in time
because of preemption.   I think in theory you are correct but  task
preemption will cause at most a 1/10 second delay and more likely
closer to 1/100th second.  The adjtime function works at uS resoltion.
 I doubt there would be a full microsecond difference in only 1/10th
second.  What we are talking about here is not the error  in the clock
but the rate of growth of the error in the clock.

-

Chris Albertson
Redondo Beach, California



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