[ntp:questions] Re: tinker step 0 (always slew) and kernel time discipline

David Woolley david at djwhome.demon.co.uk
Thu Sep 21 19:42:14 UTC 2006

In article <eeucua$5q9$1 at zcars129.ca.nortel.com>,
Joe Harvell <harvell at nortel.com> wrote:

I have an application that is sensitive to step corrections and am considering using 'tinker step 0' to disable them altogether.  However, I noticed a thread on this topic in February 2005 (http://lists.ntp.isc.org/pipermail/questions/2005-February/004468.html) that suggested setting 'tinker step 0' without explicitly using 'disable kernel' will essentially yield unpredictable behavior.

> So when "disable kernel" has been used, how is the clock frequency
> adjusted?  Also, why is the kernel time discipline disabled when a

By doing all the calculations in user space and periodically (every 4 seconds
on ntpd v3) calling adjtime to apply the slew correction for that second.
The result is a sawtoothing of the phase.

The kernel mode does the calculations every tick.

> correction of > 0.5 seconds is required?

I suspect the limit is imposed because something in the kernel overflows.

PS.  Please don't keep starting new threads for what is clearly part of
a single thread.

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