What is using my CPU systemtime?

Hi,

Since about a week top and xosview say 1 of my two CPUs is fulltime
using system-time. Loosing 1 CPU the machine is a bit sluggish, and
I'm trying to find the cause. The top program cannot display CPU
usage by system time. I wrote a little program examining
/proc/<pid>/stat for all processes, but there is no process using lots
of system CPU. I tried strace on some of the long running processes
using some user CPU, but nothing suspicious.

There is plenty of free memory, no significant disk or network activity,
no abnormal messages in /var/log/messages.

What could be using the CPU? Some form of internal kernel activity?
Is there a tool to find out?

I hate to reboot for no good reason, also because there are some long
running programs busy on the machine.

System is running SuSE 9.2, kernel 2.6.8-24.19-smp on a dual AMD Athlon.

Any clues?

Thanks --- Jan
.