[ntp:questions] Re: Getting good NTP tracking

Karel Sandler sandler at ujf.cas.cz
Thu Jun 29 07:40:44 UTC 2006


"Eino-Ville Talvala" <quantumet at gmail.com> wrote:
> Richard B. Gilbert wrote:
>> Charles Allen wrote:
>>
>>> I've lost track of who's said what, but at some point the original
>>> poster mentioned that the offset gets worse during the day.  To that I
>>> ask a question: Are the server(s) more utilized during the day?  If
>>> so, would the gurus consider lost interrupts a possibility?  Looks
>>> like CENTos uses the 2.6.x kernels which some have mentioned had
>>> trouble at least at some point in past.
>>>
>>> I mainly mention this because this has come up as a possibility
>>> several times over the previous months, and I was wondering if there
>>> is a way to diagnose this problem, either with NTP tools, or using
>>> OS tools.
>>>
>>
>> Lost interrupts result in the local clock being slow with respect to the 
>> server.  The server will fall behind, step in the positive direction, 
>> fall behind again, step, etc.  This seems to be a problem mostly with 
>> Linux systems that update the clock at frequencies greater than 100 Hz.
>> Some systems can set the update frequency to 250 or 1000 Hz and those 
>> that do so have been known to exhibit this problem.
>
> Where would I check on the clock update frequency?
>
You can cat /proc/interrupts and look for the update rate of int0. This is 
the timer.

Karel Sandler





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