[time-nuts] NTP jitter with Linux

Steve . iteration69 at gmail.com
Thu Apr 5 04:10:15 UTC 2012


It doesn't matter how fast the CPU clock rate is because you are not
dealing with a simple rate monotonicity. There are far too many
inconstancies in a PC to properly apply simple O(n) algorithms.

>Your reply ignores the simple fact that it _does_ track within a couple of
microseconds, as long as the processor is busy. The PC is _not_ the clock
source, a >PPS signal derived from GPS is. A PC is perfectly capable of 10
us accuracy. Even slower processors are capable of significantly better
accuracy

In this you are exposing a complex detail in the sampling conditions.
It is quite obvious that the experiment (The hardware,software, and
figures)
do not exhibit the precise control that you require. The more you focus,
the more problems you will find. Likewise, the mixed results you find
 from one experiment to another, strengthens the argument for
 lack of precision in the control. Whatever changes you make to increase
precision are not likely to apply to any one else.
  Those who do not see a problem are simply not objective in regards to the
scientific method. Just cargo cult science.

Steve

On Wed, Apr 4, 2012 at 11:42 PM, Mike S <mikes at flatsurface.com> wrote:

> On 4/4/2012 10:41 PM, Steve . wrote:
>
>> breaking the 1pps down as far as 10micro seconds,The
>> most obviously problem is that you are trying to use an inaccurate clock
>> source(the pc)
>>
>
> Your reply ignores the simple fact that it _does_ track within a couple of
> microseconds, as long as the processor is busy. The PC is _not_ the clock
> source, a PPS signal derived from GPS is. A PC is perfectly capable of 10
> us accuracy. Even slower processors are capable of significantly better
> accuracy - http://www.febo.com/pages/soekris/ .
>
>
>  Trying to tweak a PC to get 10microseconds (nyquist, 5microseconds max)
>>
>
> ???
>
> Maybe your PC runs in MHz, but mine runs in GHz. Are you confusing us with
> ns?
>
>
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