[ntp:questions] Support for "tickless" systems

Miroslav Lichvar mlichvar at redhat.com
Thu Nov 20 11:02:06 UTC 2014


On Thu, Nov 20, 2014 at 10:16:13AM +0000, David Taylor wrote:
> Running the sleep 10 sequence from a command procedure gives a difference of
> 1055, so I guess that's 105.5 interrupts per second.  Does sound like 100
> Hz, yes.
> 
> Running the command while another terminal was running "cat /dev/urandom >
> /dev/null" resulted in 1063 interrupts, so 106.3 Hz.
> 
> Does that mean I'm tickless or not?

It seems it's not running in the tickless mode and the problem with
zero jitter is caused by something else.

Do you have PPS kernel discipline enabled in your ntpd config (flag3)
and which driver do you use? The PPS discipline is always disabled
when the Linux kernel is compiled with NO_HZ, so I think that could
explain what you are seeing. I'm not sure if that would be an ntpd bug
or kernel bug, but I can look into it.

-- 
Miroslav Lichvar


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