[RT]adjtimex gives wrong number of ticks

[RT]adjtimex gives wrong number of ticks

[Dennis Borgmann]

Hello RT-users!

I am observing strange behaviour regarding CONFIG_HZ on various 
machines, while trying to adjust the tickrate of some systems. I found, 
that adjtimex(2) is not behaving the way it should. If I write a simple 
program like this:

#include <stdio.h>
#include <sys/timex.h>
int main() {
     struct timex t;
     adjtimex(&t);
     printf("%ld\n",t.tick);
}

, which simply is to print the time in usec between two kernel ticks, 
the output makes no sense. On a RT-System with CONFIG_HZ=1000, the 
output is "10000" and on a non-RT system with CONFIG_HZ=250 (my 
desktop-laptop), the output is "9999" - almost the same.

If I calculate correctly, it should be 1000 with CONFIG_HZ and 4000 with 
CONFIG_HZ=250.

Am i wrong, or is this an error?

Btw: adjtimex with a tick of of 1000 gives me this:

root@ap:/tmp# adjtimex --tick 1000
adjtimex: Invalid argument
for this kernel:
    USER_HZ = 100 (nominally 100 ticks per second)
    9000 <= tick <= 11000
    -32768000 <= frequency <= 32768000

on the RT-system with CONFIG_HZ=1000. This is also odd - it should print 
"USER_HZ=1000" and not "USER_HZ=100".

Strange... Any ideas?

Best regards,
Dennis