SMP and CPU1 not showing interrupts in /proc/interrupts

[James Harper]

somewhere between about 2.5.53 and 2.5.62 my /proc/interrupts has gone 
from an approximately even distribution of interrupts between CPU0 and 
CPU1 to grossly uneven:

           CPU0       CPU1       
  0:   13223321    2233217    IO-APIC-edge  timer
  1:      13442          0    IO-APIC-edge  i8042
  2:          0          0          XT-PIC  cascade
  3:     291874          0    IO-APIC-edge  serial
  8:          3          0    IO-APIC-edge  rtc
  9:          0          0    IO-APIC-edge  acpi
 14:      18932          0    IO-APIC-edge  ide0
 15:         14          0    IO-APIC-edge  ide1
 16:     190607          1   IO-APIC-level  eth0, nvidia
 17:       3214          0   IO-APIC-level  bttv0
 18:      14249          1   IO-APIC-level  ide2
 19:     121942          0   IO-APIC-level  uhci-hcd, wlan0
NMI:          0          0
LOC:   15458218   15458423
ERR:          0
MIS:          0

if i really hit the system hard then CPU1 will start accruing interrupts 
but in a mostly idle state CPU1 just sits on its bum and lets CPU0 
handle them all, with the exception of irq #0, for some reason.

any ideas?

thanks

James