[ntp:questions] Can a clock drift be too big for ntpd?

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Sat Oct 20 02:21:49 UTC 2007


>> Check the value of a Kernel variable called "HERTZ".  Some Linux systems
>> set it to 1000 which is not good for NTP.  If yours is set to 1000 (or
>> 250) try changing it to 100.
>
>More ignorance on my part.  Where would I look for this?  I searched
>the kernel source code and didn't find it.

It's probably HZ rather than HERTZ.

If you use make menuconfig...
  Processor type and features ?
       Timer frequency (250 HZ)  --->
That gets me 3 choices: 100, 250, and 1000.

That's on a 2.6 kernel.

The problem with interrupts is roughly this...
  Each time the scheduler clock ticks, the system bumps
  the time by x ms.  If the CPU is busy doing something
  else (like mucking with the file system) and doesn't get around
  to updating the clock before the next tick then a ticks worth
  of time gets lost.  That seems to match your clock always jumping
  forwards.  (But maybe I have the sign bit backwards.)

I don't know why Reiser uses a lot of CPU at interrupt level,
or even if it does.

If changing HZ fixes things, we should be sure to update the wiki.

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




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