[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Wed Jan 23 03:58:10 UTC 2008


>On recent Linux kernels, I think the drift file is always bad after reboot.
>HZ=100, no dynamic ticks aka tickless system (CONFIG_NO_HZ not set). I think
>I even tried with a kernel command line option lpj= but it didn't help.
>If the system is rebooted, ntpd stabilizes to a new different drift value.

That's a bug in the TSC calibration code.

grep your /var/log/messages* for "Detected".  You will find things like thsi:
  Jan  4 11:21:49 shuksan kernel: Detected 2793.137 MHz processor.
  Jan  4 21:30:43 shuksan kernel: Detected 2793.209 MHz processor.
  Jan 22 09:32:20 shuksan kernel: Detected 2793.139 MHz processor.

The differences in the bottom bits turn into different drift values.


Recent Linux kernels use the TSC for timekeeping.  (At least on the
systems I work with.)  There may be a simple command line option
to use another chunk of hardware.


-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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