[LinuxPPS] 100 Hz vs 250 Hz

[Cirilo Bernardo]

On Wed, Oct 15, 2008 at 5:33 AM, Luca Bertagnolio <time at berta.com> wrote:
> I've been reading about this 100 vs 250 situation, but I am unsure as to what I
> should really do in my case.
>
> I run ntpd on a Pentium MMX 200 MHz machine with 128M of RAM.  Clearly
> this machine does nothing else than ntpd, plus a few tiny services that I need
> on my home network, but they run only sporadically.
>
> For some reason, I have 250 Hz now configured in my kernel.  Should I recompile
> with 100 Hz maybe?  Would there be any benefit, or possible issues, should I
> decide to recompile with a different setting?
>
> Google didn't help me much so far... :-(
>
> Ciao, Luca
>

I'm just guessing here, but look at your kernel config information and
also the kernel source documentation.  In the kernel config you need
to select the timer frequencies available:

# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250

If it is possible to set multiple CONFIG_HZ_* values, it may be
possible to specify which one to use at run-time.  Otherwise you do
need to rebuild.  I tried to check and discovered that this desktop of
mine only has a 2.6.11 kernel source (which has been obsolete for a
few years now).

- Cirilo