Behaviour of a cyclic task with HZ = 1024

From: Peter Mueller (
Date: Mon Sep 04 2000 - 03:25:09 EST


I have set the HZ constant to 1024 to increase the select resulution.
But the results of my measurements are not
as expected. I have a cyclical task (using select for timing) that
inverts a parallel port bit in each
cycle. I measure the high time with an oszillograph.

Here are my results:

15ms cycle: Everything as expected. The jitter is around 1ms
(corresponds to the 1000Hz).
10ms cycle: The cycle is either 10ms or 20ms. No values between.
5ms cycle: The cycle is either 10ms or 15ms. No values between.

Do you have any explanations for this behaviour? Is there a better way
to increase to resolution of the select call? Do I have to modify any
parameters in the scheduler code?


P.S: I found that the HZ constant is used in the tcp code. Do I have to
expect any errors coming from the changed HZ value?

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at

This archive was generated by hypermail 2b29 : Thu Sep 07 2000 - 21:00:17 EST