sparc 2 usable interrupt load?

["Aaron J. Grier" <agrier%poofygoof.com@localhost>]

I've been running 1.6.1 on a trusty sparc2 for years.  it handles
routing and NAT duties, but after increasing load on my wireless
segment, it seems to be melting down just passing packets:

le0 at sbus0 slot 0 offset 0xc00000 level 4 (ipl 5): address 08:00:20:11:56:75
le0: 8 receive buffers, 2 transmit buffers
le1 at sbus0 slot 1 offset 0xc00000 level 5: address 08:00:20:11:56:75
le1: 8 receive buffers, 2 transmit buffers
le2 at sbus0 slot 2 offset 0xc00000 level 5: address 08:00:20:11:56:75
le2: 8 receive buffers, 2 transmit buffers

vmstat -i:

interrupt                                     total     rate
lev1                                      404051709       36
lev3                                       63835545        5
lev5                                      942141929       85
lev6                                           1507        0
clock                                    1097372546       99
lev12                                         34030        0
prof                                     1097186333       99
zs0 intr                                      34030        0
esp0 intr                                 280432982       25
Total                                    3885090611      354

this with 98+% interrupt time according to top.  interactive shell
through an ssh session is extremely laggy.  the bulk of traffic flows
are between le2 and le0.

I realize this is only a 40MHz machine, but I would have thought it able
to pass 10mbit traffic at close to wire speed.  am I mistaken?  have I
really hit the performance limit?  (could an ISA 486SLC do better?)

-- 
  Aaron J. Grier | "Not your ordinary poofy goof." | 
agrier%poofygoof.com@localhost