[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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