Interrupt storm

[Dima Veselov <kab00m%lich.phys.spbu.ru@localhost>]

Greetings,

I have two identical Dell R220 servers running NetBSD 8-STABLE
and they are working fine, but I noticed permanent high CPU
usage.

This always look like this:

75 processes: 71 sleeping, 1 stopped, 3 on CPU
CPU0 states:  0.0% user,  0.0% nice,  0.7% system, 84.9% interrupt, 14.4% idle
CPU1 states:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU2 states:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU3 states:  0.0% user,  0.0% nice, 62.3% system,  0.0% interrupt, 37.7% idle
Memory: 3564M Act, 180K Inact, 7288K Wired, 83M Exec, 3020M File, 3272M Free
Swap: 2048M Total, 2048M Free

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
    0 root      96    0     0K   23M CPU/3     70.0H 79.15% 79.15% [system]

All other processes take 0% of anything. 
System and interrupt percentage differ from time to time, but
it always take up to 100% of one core.

I think this is kind of a driver problem, but how can I identify
which hardware cause that load? 

Thanks in advance.

-- 
Sincerely yours,
Dima Veselov
Physics R&D Establishment of Saint-Petersburg University