[ntp:questions] SO_TIMESTAMPING experiments (sub-us jitter over LAN)

gabs gsricalde at gmail.com
Thu Oct 18 11:43:02 UTC 2012


On Thursday, October 18, 2012 6:40:01 PM UTC+8, Miroslav Lichvar wrote:
>
> NTP supports interleaved mode in peer associations which does the
> timestamp followup. It would be really nice if ntpd supported the
> SO_TIMESTAMPING option.
> 
> http://www.eecis.udel.edu/~mills/ntp/html/xleave.html
> 

Days of lurking Dr. Mills' site and I didn't notice that.

>
> You may want to try nohz=off, it seems there is a bug in the kernel 
> which can cause an extra jitter of couple microseconds in the 
> system clock readings when the system is idle. 
>

Must be the reason why one of my Atom machines needs a process looping
a 10 ms sleep to bring the PPS jitter down.

>
> > 91509  509
> > 89577 -991
> > 88365 -795
> > 89574 -731
> > 90593 -163
> > 89360 -1067
> 
> > 
> > 92650 -318
> > 90634 -910
> > 89455 -989
> > 89511 -1080
> > 88874 -693
> > 88534 -1140
> 
> Cool. Are those numbers nanoseconds?
> 

Original post is wrong, those are nanoseconds.



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