iwn: Intel Centrino 6205 bad 11n performance

[Johannes Dieterich]

Dear all,

I have a Intel Centrino Advanced-N 6205 WLAN NIC in my Thinkpad using iwn.

iwn0 at pci0:3:0:0:    class=0x028000 card=0x13118086 chip=0x00858086 rev=0x34
hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Centrino Advanced-N 6205 [Taylor Peak]'
    class      = network

Unfortunately, I only get a rather bad speed using CURRENT (r270098) out of
the chip. It is connected to an 11n (on the 2.4 GHz band) network:

wlan0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
    nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
    media: IEEE 802.11 Wireless Ethernet MCS mode 11ng
    status: associated
    ssid XXXXX channel 4 (2427 MHz 11g ht/20) bssid XXXXXXXXXX
    country US authmode WPA2/802.11i privacy ON deftxkey UNDEF
    TKIP 2:128-bit txpower 15 bmiss 10 scanvalid 60 bgscan bgscanintvl 300
    bgscanidle 250 roam:rssi 7 roam:rate 64 protmode CTS ampdulimit 64k
    ampdudensity 8 -amsdutx amsdurx shortgi wme roaming MANUAL

I get a maximum of 900 KB/s of throughput (both in/out, approximated by
copying a large file using scp), within the network and to the outside
world. Running SuSE Linux on the notebook allows me to easily saturate my
uplink at > 3MB/s, didn't then further check within the network. I get no
log messages on FBSD from iwn and I am not located in a particularly noisy
neighborhood.

The only performance issue I can find with this chip is one old report on
Ubuntu (http://ubuntuforums.org/showthread.php?t=1949571), where the 11n
seemed to be the culprit in the driver/firmware. Could this be an issue for
us as well (firmware problem?)?

As my workhorse is FreeBSD, I'd love to fix this issue. How can I further
debug this issue and/or provide more data? I know that the status of iwn in
FBSD is difficult ATM but maybe there is hope?

Best

Johannes