[ntp:questions] Re: Ntp-4.1.2: tinker step 0;always slew and kernel time discipline

Nikolaev, Sergey snikolaev at ebs.com
Fri Feb 18 14:52:08 UTC 2005


Dave,

Thanks for your replies. Actually, I have just got data from my tests
and this is what I am observing.
If "tinker step 0" but the "kernel" is not disabled explicitly, a
20-second offset 
(set manually via the date command) is corrected at a rate of about 0.5
millisecond/s as expected, 
but overshoots the right time by about the same absolute value of
offset. This happens repeatedly. 
For example, from -20 sec it goes all the way to 20 sec offset and then
back to -20 and so on many times. 
I did not wait for it to settle down. 

When the "kernel" is disabled, it overshooted only by less than 0.5s and
then slowly settled to the correct time.
Actually, it settled to the range of +-120ms around the peer's time.

It looks to me that "disable kernel" offers a saner behavior in this
case.
Any comments?

Regards,
Sergey

-----Original Message-----
From: questions-bounces at lists.ntp.isc.org
[mailto:questions-bounces at lists.ntp.isc.org] On Behalf Of David L. Mills
Sent: Thursday, February 17, 2005 9:24 PM
To: questions at lists.ntp.isc.org
Subject: [ntp:questions] Re: Ntp-4.1.2: tinker step 0;always slew and
kernel time discipline


Nikolaev,

In truth, the kernel is disabled only if the actual correction is 
greater than 0.5 s no matter what the tinker. However, there could be 
grief if the discipline switches from one to the other. There are a 
rather large number of untested and probably dangerous things that might

happen with uncharted combinations of tinkers and I'm not thrilled when 
spending lots of time fixing the broken combinations. You are on your 
own, but a "diable kernel" command might be appropriate.

Dave

Nikolaev, Sergey wrote:
> We have a requirement to always slew the clock even if it means long 
> periods of time to correct the offset.
> 
> The NTP documentation mentions this tinker option:
> 
> step step
> The argument is the step threshold, by default 0.128 s. It can be set
to any positive number in seconds. If set to zero, step adjustments will
never occur. 
> Note: The kernel time discipline is disabled if the step threshold is
set to zero or greater than the default.
> 
> However when I set "tinker step 0" and restart ntpd, I see in "ntpdc 
> -c sysinfo" that the kernel flag is still enabled. Obviously, it is 
> not disabled automaticly just by setting "tinker step 0".
> 
> Do I need to disable it explicitly?
> 
> Thanks in advance,
> Sergey
> 
> 


































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