latency spikes, was Re: [LinuxPPS] slightly offtopic

[gnu not unix]

(waves) 'Morning from California *sips coffee*

In message <451FCA61.8090305 at xs4all.nl> you write:

>Hello,

>Not really pps related, but how would you fix the situation where you
>gps works OK but is not chosen as the time source?

(...)

>So how come?

># ntpq -pn
>     remote           refid      st t when poll reach   delay   offset jitter
>==============================================================================
> 127.127.1.0     .LOCL.          10 l    9   64  377    0.000    0.000 0.002
>x127.127.20.0    .GPS.            0 l    -   16  377    0.000  -165.88 3.688
(...)
(big list of remote peers deleted)

Your offset is Rather High. And the jitter is large also. 

So, the normal ntp mitigation has decided that the remote host
has the One True Tick and thus, has been chosen as peer.

Were you running a disk io test or doing a lot of console (not X-windows)
scrolling? Heavy disk io will tend to clobber your offset/jitter.

The bare VGA scrolling (not in a window system just the console "terminal")
is about the worst for latency spikes and jitter. I usually ssh in when
working on hosts, rather than use a bare console. 

../Steven