I've had performance problems with garbage collection before, but this profiler output gave me a great giggle:

  00000030 6173     2.26089     ipt_do_table_Rsmp_b731682a /lib/modules/2.4.18-26.7.xcustom/kernel/net/ipv4/netfilter/ip_tables.o
  c01dc450 11798    4.32107     rt_intern_hash          /logs/vmlinux
  00000000 25777    9.44095     (no symbol)             /isd/isdwss/erts-5.2.b1.oprofile/bin/beam
  c01ddfa0 40883    14.9736     ip_route_input          /logs/vmlinux
  c01d0a60 109002   39.9225     neigh_forced_gc         /logs/vmlinux

Time for a generational collector in Linux? :-)

And I must say, oprofile is an unbelievably cool tool. Who says systems software research is irrelevant?

(P.S., that GC expense is provoked by a flood of IP packets with random source addresses.)