[LinuxPPS] Re: strange readings...

[Martin]

On Fri, May 18, 2007 at 07:52:35AM +1000, James Boddington wrote:
> These my HZ settings. I am trying NO_HZ using the master branch from 
> linuxpps.
> 
> CONFIG_NO_HZ=y
> CONFIG_HZ_100=y
> # CONFIG_HZ_250 is not set
> # CONFIG_HZ_300 is not set
> # CONFIG_HZ_1000 is not set
> CONFIG_HZ=100


You say you are using NO_HZ, but you also have HZ_100
selected. Does the NO_HZ overide the other?

 
> I am happy enough with results.
> 
> http://aiken.dnsalias.org/cgi-bin/ntp has offset and drift
> graphs for my ntp server and 2 of the client machines. The
> bad bits in the graphs for sunday and monday are because I
> changed from freebsd back to linux for ntp and it took a
> couple of days before I was happy with it.
> 
> 2.6.21 still can not follow the 1pps from the garmin as
> well as 2.6.17 and earlier or freebsd can but it is still
> doing better than 2.6.18 - 2.6.20.

Any clue why?


> I use the SHM driver as the preferred peer. I read 16
> offsets, drop the outliers and average the rest then use
> the shm driver to feed the time to ntp. My hardware has a
> nasty habit of generating large offsets. Had a 100ms and a
> 129ms offset last night on the pps. The worst has been 1.3
> seconds.  This happens under both linux and freebsd.

Just so I am following, you wrote something to collect the
information from the linuxpps using the netlink interface
and then use the shm driver to feed the time to ntp?

Is there any reason you do this instead of using the nmea
driver? Is it so you can drop the outliers? Your output
lists the nmea driver as well and the offset/jitter looks
the same.


> The reason for minpoll 4 maxpoll 4 for pebbles is ntp
> makes a useful
> thermometer. http://aiken.dnsalias.org/cgi-bin/ambient

Nice! :D


Martin.