Bridging atheros/ethernet seems incredibly slow

[Nate Nielsen]

Has anyone else seen a problem where bridging an Atheros wireless with
an ethernet interface has painfully slow throughput?

I have two boxes sitting next to each other both running FreeBSD 6.0.

   BOX 1          BOX 2
---- A +++++++++++ B/C -----

Two Atheros (5213) 802.11a cards (A and B above) are connected to each
other using adhoc mode. I can get roughly 10+ Mbps of throughput between
A and B (measured using iperf, flood pings, simple tcp transfer).

One box has it's wireless NIC (ie: B above) bridged with an ethernet
interface (ie: C above).  Throughput to the ethernet nic is nice and
high (20+ Mbps).

However when sending traffic through the bridge, the transfer rate drops
below 500Kbps.

Non issues:
- The CPU's on neither box are being taxed.
- I've tried both bridge(4) and if_bridge(4). Same results.
- Locking down the wireless speed doesn't help (just a wild guess).

Interesting things:

Running 'ifconfig ath0 list sta' on BOX 1 shows all sorts of mac
addresses on the BOX 2 side of the network. The first is the wireless
adhoc peer. Maybe that's to be expected:

> ADDR               AID CHAN RATE RSSI IDLE  TXSEQ  RXSEQ CAPS ERP
> 00:01:b4:02:0d:e7    0   52   6M   43    0    258  33072 I      0
> 00:30:48:76:55:4a    0   52   6M   43   15      7  32016        0
> 00:11:43:d1:07:7d    0   52   6M   43   15      0  32528        0
> 00:48:54:70:10:09    0   52   6M   44   45      0  26368        0
> 00:0e:a6:91:60:c1    0   52   6M   44  105      0  16576        0
> 00:a0:cc:5e:b0:b6    0   52   6M   43   15      0  31344        0
> 00:20:ed:60:58:ac    0   52   6M   43  180      0   5600        0
> 00:0b:db:a3:68:91    0   52   6M   42  150      0  10688        0
> 00:0d:61:37:3e:36    0   52   6M   43  120      0  14896        0
> 00:02:e3:08:8b:d1    0   52   6M   41   45      0  28112        0

Doing a flood ping from BOX A to a machine bridged across the link is
not lossy, instead the send rate is limited. That is, the ping packets
are sent slowly.

athstats on BOX 2 shows:

> 13 tx management frames
> 7 tx frames discarded prior to association
> 544 tx failed 'cuz too many retries
> 6014 long on-chip tx retries
> 876 tx frames with no ack marked
> 1952 rx failed 'cuz frame too short
> 5129 rx failed 'cuz of PHY err
>     1524 OFDM timing
>     3605 OFDM illegal rate
> 1 beacons transmitted
> 91 periodic calibrations
> rssi of last ack: 36
> avg recv rssi: 38
> 1 switched default/rx antenna
> Antenna profile:
> [1] tx     1192 rx    18513
> [2] tx       68 rx        1

Anyone have any ideas on where I should look for the problem?

Cheers,
Nate