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

Joe Harvell harvell at nortel.com
Fri Sep 22 16:58:33 UTC 2006

David L. Mills wrote:
> Joe,
> "disable kernel" does exactly and precisely that. In that case 
> corrections are handled as if the kernel code does not exist.
> Ordinarily, to disable the step correction also disables the kernel. 
> Your "tinker step 0" exposed a bug, now fixed, in which the kernel was 
> not automatically disabled in that case.

In the Feb, 2005 thread, you stated that the kernel was disabled exactly if the amount of the correction was >0.5 seconds and hand nothing to do with the step threshold.

Do you happen to know in which release of ntp the behavior was changed to what you are describing now?

> Dave
> Joe Harvell 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 what does disable kernel do?  Does it disable the NHPFL algorithm?  
>> Is this algorithm synonomous with the "kernel time discipline?"  So 
>> when "disable kernel" has been used, how is the clock frequency 
>> adjusted?  Also, why is the kernel time discipline disabled when a 
>> correction of > 0.5 seconds is required?
>> ---
>> Joe Harvell

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