Kernel NTP flipping between FLL and PLL modes

Andriy Gapon avg at
Tue Apr 5 05:03:46 PDT 2005

on 01.04.2005 20:40 Bob Bishop said the following:
> Unlikely I think. As I said, I've got several machines on the same LAN:
> the 5.3's misbehave; the others don't.

#define       CLOCK_ALLAN     1500.
double        allan_xpt = CLOCK_ALLAN;
if (ULOGTOD(sys_poll) > allan_xpt / 2) {

if I understand the above "random" lines of code in
contrib/ntp/ntpd/ntp_loopfilter.c correctly, then PLL<->FLL switch
occurs when polling interval goes 512<->1024, which is perfectly
possible under certain conditions with default ntp settings: minpoll=64,
maxpoll=1024 if ntp.conf(5) can be trusted.

BTW, "tinker allan" part of the man page seems to not be correct - it
has 1024 for default value when the code has 1500 as you can see.

As I understand between 5.2.1 and 5.3 ntpd version changed from 4.1.1b
to 4.2.0 and changes in this PLL/FLL area were significant, so I am not
sure what is right and what is wrong here but I am going to experiment
with tinker-ing allan to 2048 as Christian Hiris has suggested:

P.S. BTW, what rules polling interval value increase/decrease ?

Andriy Gapon

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