Yo Miroslav!
On Tue, 3 Mar 2015 10:28:37 +0100
Miroslav Lichvar <mlich...@redhat.com> wrote:
> On Tue, Mar 03, 2015 at 12:38:41AM -0800, Gary E. Miller wrote:
> > > > Ah, that explains a lot. Will that fix the jitter computation?
> > >
> > > Yes, the +/- value in the chronyc sources output should be smaller
> > > than 1 us now. It's mostly a cosmetic issue, it likely won't have
> > > any noticeable effect on the synchronization. The precision is
> > > the minimum allowed value of dispersion to avoid zero dispersion
> > > with low resolution refclocks, e.g. with microsecond SHM it is
> > > possible to get several samples with 0 offset, the dispersion
> > > would be zero and it would then break all kinds of things.
> >
> > Oh, great.
> >
> > First, why does chronyd not support uSec SHM? (I usually use the
> > SOCK)
>
> It does support both microsecond and nanosecond resolution in SHM.
Very odd. That is not what I have been seeing, so instead of unimplemented
it must be broken.
The
> default value of precision is set for microseconds, because using
> nanosecond resolution with microsecond precision is much better than
> using microsecond resolution with nanosecond precision as some samples
> could have three orders of magnitude smaller dispersion that others.
Yeah, I already went back and fixed the howto and my configs. Still
no nSec on chronyd SHMs, but it works on ntpd.
> > Two, so if I make it perfect (zero offset) things break?
>
> No, I was just trying to explain that the refclock precision prevents
> that problem. If several consecutive refclock samples have identical
> offset, the calculated dispersion might be zero, but it will be set
> to the precision before accumulating the sample to avoid division by
> zero etc.
So if the offset is zero it is set to the dispersion? That is not good.
Most people just set the precision approximately and get much better
jitter/offset than that. When they hit the nail on the head this
will add back a lot of 'jitter'. Hitting your thummb.
RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
g...@rellim.com Tel:+1(541)382-8588
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