[ntp:questions] NTP not syncing

mike cook michael.cook at sfr.fr
Sat Nov 2 23:42:31 UTC 2013


Le 2 nov. 2013 à 23:47, antonio.marcheselli at gmail.com a écrit :

> 
>> 
>>> You might check whether the system boards do power saving by changing cpu clock frequencies. That throws ntpd. 
>> 
>>> 
>> 
>> 
>> 
>>  Some more info in the same vein. This issue has been seen with Supermicro boards as far back as 2006.
>> 
>> Check out the following to see if your linux is configured to manage cpu stepping. If you don't see it there, disable it in the BIOS.
> 
> 
> 
> This is interesting.
> Are you saying that if the CPU is changing frequency and Linux is not configured to handle it, ntpd will see the clock changing wildly?

  That's about it. One of the assumptions made by NTP is that it is running at a fixed clock speed (or rather that the system 'clock source' is). So when that sources frequency is altered for power saving or performance enhancement (you can configure both) , it will be seen as slowing or speeding up  when compared with the configured servers timestamps. If for instance, after booting and ntp startup the cpu goes idle, then the frequency could be lowered, causing the clock source to slow down, causing your problem. In older implementations I believe that the cpu frequency lowering also caused the clock source to slow (ex. the TSC was directly linked to the cpu frequency) but I believe that some newer cpus keep the clock source running at a constant frequency and just modify the execution units frequency to avoid this issue. 

> 
> Thanks,
> Antonio
> 
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