How to obtain which interrupts cause system to hang?

[b. f.]

> How to obtain what nasty happen, which process take 36-50% of CPU
> resource?

It partly depends upon the version of the OS that you are running,
your hardware, and your configuration. 2008 interrupts/sec is high,
but not improbably so, for kern.hz>=1000, and not beyond the
capabilities of today's average computer, although it may not be
optimal for your workloads.  So it may not actually be a problem with
too many interrupts, but rather with some erroneous system accounting.
 This can happen, for example, if your computer is using some of the
deeper power-saving C-states, but using them poorly, as for example
in:

http://lists.freebsd.org/pipermail/freebsd-current/2010-August/019383.html

So you may want to examine, and perhaps adjust, your choice of kernel
timers, kern.hz, and power-saving settings.  Device polling can also
be a factor, if you are using it.

b.