[ntp:questions] Re: Getting good NTP tracking

Richard B. Gilbert rgilbert88 at comcast.net
Thu Jun 29 00:41:08 UTC 2006


Eino-Ville Talvala 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?
> 

There is a kernel parameter called HZ.  Check its value.  If the value 
is greater than 100 try changing the value to 100.




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