Linux Socket Filter sudden CPU use increase

From: Eduardo Magaņa Lizarrondo (
Date: Tue Feb 27 2001 - 15:42:25 EST

I have been testing Linux Socket Filters (LSF) these weeks (kernels
2.2.14, 2.2.18, 2.4.1) with libpcap (0.4 - 0.6.2) and I have observed
something curious. I make a program that increase number of simultaneous
LSF filters (5, 10, 15..) and when this number is between 15 and 50,
CPU consumed by kernel increases suddenly. Any idea?
(you can see a figure of CPU vs. number of LSF filter in

I do not see anything stranger. Only, using Linux Trace Toolkit with
modifications when there are few filters, I observe that of timer Bottom
follows IRQ 0. And when there are more filters, IRQ 0 takes place when
network Bottom Half is taking place, so the timer Bottom Half is delayed
the end of the network Bottom Half. Can it be related?

To measure kernel CPU I have used the trick of running another CPU with
priority. According to the time this second process is delayed an
%CPU is obtained.

I do not understand what is happening. Any help would be very useful.


Eduardo Magaņa Lizarrondo
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Wed Feb 28 2001 - 21:00:15 EST