convert jiffies to seconds

Question

I've got a piece of userspace code which is parsing /proc/PID/task/TID/stat to get the cpu usage. I can use HZ to get the jiffies per second but this code could move to another machine which has a different configured value. Is there any way to get the value of HZ from userspace at runtime?

Answer 1

You divide it by the number you get from sysconf(_SC_CLK_TCK).

However, I think this is probably always 100 under Linux regardless of the actual clock tick, it's always presented to userspace as 100.

See man proc(5).

Answer 2

To clarify the math behind MarkR's answer:

sysconf(_SC_CLK_TCK) will get you jiffies per second. Divide jiffies by the number you get from sysconf(_SC_CLK_TCK) to get the total number of seconds.

      jiffies                      jiffies              seconds
--------------------    =     -----------------    =    -------    =    seconds
sysconf(_SC_CLK_TCK)          (jiffies/second)             1