[ntp:hackers] Time constant too large?

David L. Mills mills at udel.edu
Thu Jan 3 00:42:56 UTC 2008


Brian,

P l e a s e check the tick interrupt frequency. I suspect it is higher 
than 100 Hz, in which case as I said before, the frequncy gain is way 
too high.. The Alpha Tru64 has been running the microkernel since 1992 
with no ill effects. Note that its timer frequency is 1024 Hz and that 
the frequency gain has been calibrated for that frequency.

Dave

Brian Utterback wrote:

> I have been testing the V4 code on Solaris Nevada, and have notice
> something rather disturbing. On one system I have that has a measured
> frequency correction of 28.5 ppm, it takes the version 3 xntpd about
> an hour to get to plus or minus 2 or 3, and then settles on 28.5 in about
> 10 hours. However, the V4 code jumps to something between 40 and 60,
> and then slowly moved towards 28.5 over about a week and a half. This
> is not acceptable performance and is a showstopper for upgrading to
> the latest builds in Solaris.
>
> Now, looking at some of the documentation that Dave has published, there
> is a mention that if you run a micro kernel with the V4 code the time 
> constant
> will be too big. Could this be the problem? Solaris is indeed using 
> the micro
> kernel ntp_adjtime. If it is, I would think that it would be possible 
> to correct
> for this at run time.
>
> Oh, and if :disable kernel" is configured, then the V4 code gets the 
> right value
> in just a few hours, just like the V3 code. Any ideas on how to fix this?
>
> Brian Utterback




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