✘sys_fuzz * ntp_random()

[Achim Gratz]

Gary E. Miller writes:
> Last week we had a discussion on sys_fuzz and the value of adding
> random noise to some measurements.  The code defi2nes sys_fuzz asL
>
>     "* The sys_fuzz variable measures the minimum time to read the system
>      * clock, regardless of its precision."
>
> Rondomness of half the sys_fuzz is then added to some values, like this:
>
>     fuzz = ntp_random() * 2. / FRAC * sys_fuzz
>
> Makes no sense to me.  Adding randomness helps when you have hysteresis,
> stiction, friction, lash and some other things, but none of those apply
> to NTP.

https://en.wikipedia.org/wiki/Dither

You might have enough other noise in any particular system so the
sys_fuzz (which whitens the quantization noise on the clock reading)
doesn't make a difference or you might not.  But presumably Dave Mills
didn't put it in there just because he was trying to add useless code.

> So I took two identical RasPi's and forced sys_fuzz to zero on one of
> them.  Four days later I can see no difference in the results from
> those two.

Which proves exactly nothing.


Regards,
Achim.
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