[ntp:questions] Clock and Network Simulator

Miroslav Lichvar mlichvar at redhat.com
Thu Jul 1 13:27:18 UTC 2010

On Wed, Jun 30, 2010 at 10:00:06PM +0000, David L. Mills wrote:
> The change in SHIFT_PLL would result
> in unstable behavior below 5 (32 s), as well as serious transients
> if the discipline shifts from the daemon to the kernel and back. All
> feedback loops become unstable unless the time constant is at least
> several times the frequency update interval, which is this case is
> one second. If you do want to explore how stability may be affected,
> restore the original design and recompile the distribution with
> NTP_MINPOLL changed from 3 to 1.

I recompiled ntpd with NTP_MINPOLL 1 and here is a PLL response plot
for SHIFT_PLL 4 poll 1 and SHIFT_PLL 2 poll 3:


The initial offset is 0.1 second, after crossing zero offset, they
both stay in negative.

Miroslav Lichvar

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