Yo Eric! On Thu, 19 Jan 2017 17:23:01 -0500 "Eric S. Raymond" <e...@thyrsus.com> wrote:
> Gary E. Miller <g...@rellim.com>:
> > Yo Eric!
> >
> > On Thu, 19 Jan 2017 14:30:35 -0500
> > "Eric S. Raymond" <e...@thyrsus.com> wrote:
> >
> > > Gary E. Miller <g...@rellim.com>:
> > > > > - to fuzz the low-order bits of the clock.
> > > >
> > > > Hmm, can you expand on this a bit? Which clock? How much fuzz?
> > > > Does this degrade anything?
> > >
> > > Whenever ntpd polls the system clock, it fuzzes the lowest-order
> > > digits of the result. The amount of fuzz to apply is bounded by
> > > half the measured interval between system clock ticks.
> >
> > Hmm, and how much would that typically be?
>
> I...don't actually know. Probably less than a microsecond.
I little less than a micro Second would concern me. A lot less would
not.
> It
> should be available as the value of the system variable
> "fuzz" (internally sys_fuzz) but I see
>
> ntpq> rv 0 fuzz
> fuzz=0.001
>
> which makes me suspect a units problem somewhere.
ntpd/ntp_proto.c line 2639 says the units are Seconds. If true
that makes your sys_fuzz 1 milli Second. So adding a bit of randomness
around 500 micro Seconds. That is terrible. 500x worse than we can
see in the PPS refclock.
> > Can you point me to this code? I want to rip it out and do a
> > test.
>
> libntp/systime.c
On line 65 it says that sys_fuzz is in seconds! That agrees with
ntp_proto.c. So still terrible.
> Have fun. You'll probably do a better job of ayditing that code than
> I would.
Very interesting stuff. It will have to wait until the libsodium
thing is put to bed.
RGDS
GARY
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