[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.

More information about the questions mailing list