How to bench your interrupts in 8 easy steps:

1) apply the patches for your FreeBSD version (4 for 4.x, 7 for HEAD)
2) add KERN_TIMESTAMP to your KERNCONF
3) buildkernel && installkernel

4) 
 ONLY for 7.x:
 o select the irq you want to track down via debug.source
   (i.e. to track down irq 9 "sysctl debug.source=9")

 ONLY for 4.x:
 o 4-icu_vector.s.patch has hardcoded to track down irq 9
   (look in ptstmp:)

5) do some network traffic
6) sysctl -b debug.timestamp > tstamp.data
7) tsc.sh tstamp.data > tstamp.txt
8) build your own graphs