[2.5.73] What causes this high interrupt count?

Hi,

With 2.5.73 with ACPI enabled on my P4 HT system irq 18 seems to be very busy:
CPU0 CPU1

  0:     633529      76869    IO-APIC-edge  timer
  2:          0          0          XT-PIC  cascade
  9:          0          0   IO-APIC-level  acpi
 14:      12139          0    IO-APIC-edge  ide0
 15:          2          0    IO-APIC-edge  ide1
 16:      58707          0   IO-APIC-level  uhci-hcd, uhci-hcd, nvidia
 17:      56840          0   IO-APIC-level  Intel ICH5
 18:   88494437   48181320   IO-APIC-level  ide2, uhci-hcd
 19:      15975          0   IO-APIC-level  uhci-hcd
 20:        183          0   IO-APIC-level  ohci1394
 21:       1647          0   IO-APIC-level  eth0
 23:         68          0   IO-APIC-level  ehci_hcd
NMI:          0          0
LOC:     710285     710628
ERR:          0
MIS:          0

ide2 is the onboard Intel SATA (ICH5) controller. I am not sure what is causing these interrupts.

Top shows a lot of CPU load being generated caused by the high interrupt count:

81 processes: 80 sleeping, 1 running, 0 zombie, 0 stopped
CPU0 states: 2.0% user 58.0% system 0.0% nice 0.0% iowait 40.0%
idle
CPU1 states: 3.0% user 0.0% system 0.0% nice 0.0% iowait 97.0%
idle
Mem: 515480k av, 198452k used, 317028k free, 0k shrd, 14760k
buff

       122252k active,              50596k inactive

Swap: 787176k av, 0k used, 787176k free 94040k
cached

I've had the same problem with 2.4.21 plus a recent ACPI. What can be the culprit?

Cheers,

Jurgen