[ntp:questions] Allan deviation survey

David L. Mills mills at udel.edu
Fri Sep 10 22:28:34 UTC 2010


David,

I beg to differ. All the machines I used are PCs or similar 
workstations. They really and truly behave according to an exponential 
distribution with a small mean of a few to a few tens of microseconds. I 
have done a tedious histogram from which I can pick out the cache 
replacement, context-switch and timer interrupts. I've used both uniform 
and exponential noise models with substantially the same results. Since 
I was looking for the best performers, most of the data was collected on 
lightly loaded machines; the characteristics with a heavily loaded 
campus server are much worse.

Dave

David Woolley wrote:

> Miroslav Lichvar wrote:
>
>>
>> A very useful statistics is the Allan deviation. It can be used to
>> compare performance of oscillators, to make a guess of the optimal
>
>
> Surely that is based on a particular model of the phase noise and the 
> big argument about ntpd is that PC's don't follow that model.
>
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