WMM caused packet loss with ath9k

Sun Aug 25 03:03:35 PDT 2013

Hello,

I hope this is the right outlet for my shouts for help. I am trying to 
run a 802.11n 5GHz AP from a tl-wdn4800 pci-e 3x3 adapter which seems to
contain a AR9380 chipset.

With disabled wmm (wmm_enabled=0), I get reliable connection at 54 Mb/s,
1-4ms ping with no apparent packet loss, and around 17 Mb/sec actual
transfer rate: 
[  3]  0.0- 1.0 sec  2.12 MBytes  17.8 Mbits/sec
[  3]  1.0- 2.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  2.0- 3.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  3.0- 4.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  4.0- 5.0 sec  2.12 MBytes  17.8 Mbits/sec
[  3]  5.0- 6.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  6.0- 7.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  7.0- 8.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  8.0- 9.0 sec  2.00 MBytes  16.8 Mbits/sec
[  3]  9.0-10.0 sec  2.12 MBytes  17.8 Mbits/sec

When I enable wmm, I get faster connection (up to 270 Mbit/s)
with significant packet loss which seems to come every few 
seconds for a second or more: 

[  3]  0.0- 1.0 sec  9.12 MBytes  76.5 Mbits/sec
[  3]  1.0- 2.0 sec  4.75 MBytes  39.8 Mbits/sec
[  3]  2.0- 3.0 sec  3.38 MBytes  28.3 Mbits/sec
[  3]  3.0- 4.0 sec  3.25 MBytes  27.3 Mbits/sec
[  3]  4.0- 5.0 sec  6.25 MBytes  52.4 Mbits/sec
[  3]  5.0- 6.0 sec  3.50 MBytes  29.4 Mbits/sec
[  3]  6.0- 7.0 sec  3.12 MBytes  26.2 Mbits/sec
[  3]  7.0- 8.0 sec  6.38 MBytes  53.5 Mbits/sec
[  3]  8.0- 9.0 sec  0.00 Bytes  0.00 bits/sec
[  3]  9.0-10.0 sec  6.62 MBytes  55.6 Mbits/sec
[  3] 10.0-11.0 sec  0.00 Bytes  0.00 bits/sec
[  3] 11.0-12.0 sec  1.12 MBytes  9.44 Mbits/sec
[  3] 12.0-13.0 sec  5.25 MBytes  44.0 Mbits/sec
[  3] 13.0-14.0 sec  6.38 MBytes  53.5 Mbits/sec
[  3] 14.0-15.0 sec  3.25 MBytes  27.3 Mbits/sec
[  3] 15.0-16.0 sec  3.75 MBytes  31.5 Mbits/sec
[  3] 16.0-17.0 sec  0.00 Bytes  0.00 bits/sec
[  3] 17.0-18.0 sec  0.00 Bytes  0.00 bits/sec
[  3] 18.0-19.0 sec  6.88 MBytes  57.7 Mbits/sec
[  3] 19.0-20.0 sec  0.00 Bytes  0.00 bits/sec
[  3] 20.0-21.0 sec  0.00 Bytes  0.00 bits/sec
[  3]  0.0-21.4 sec  73.1 MBytes  28.6 Mbits/sec

This doesn't seem to be just QoS load prioritizing, 
since ping in a no-load situation has similar issues:

64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=6.14 ms
64 bytes from 10.0.0.1: icmp_seq=2 ttl=64 time=2.85 ms
64 bytes from 10.0.0.1: icmp_seq=3 ttl=64 time=5.03 ms
64 bytes from 10.0.0.1: icmp_seq=4 ttl=64 time=3.79 ms
64 bytes from 10.0.0.1: icmp_seq=5 ttl=64 time=3.66 ms
64 bytes from 10.0.0.1: icmp_seq=6 ttl=64 time=2.50 ms
64 bytes from 10.0.0.1: icmp_seq=13 ttl=64 time=2.54 ms
64 bytes from 10.0.0.1: icmp_seq=17 ttl=64 time=2.96 ms
64 bytes from 10.0.0.1: icmp_seq=18 ttl=64 time=7.66 ms
64 bytes from 10.0.0.1: icmp_seq=19 ttl=64 time=3.22 ms

Both clients, running Intel Ultimate-N 6300 3x3 cards, 
are affected. The wireless spectrum seems to be more or less clear 
containing only 2 other weak 5GHz APs, both on Channel 44
compared to my 48. 

Is this a known issue? I couldn't find any mention of it. 
Can someone point me at what I should try? I tried 
using a different channel but I did not see any change 
in behavior. 

Thanks! 

Rasto

====================================================
Versions/Configuration: 

Client: 
Debian, vanilla 3.9.8 kernel, wpa_supplicant 1.0-3+b2
Server: 
Debian, debian 3.10-2-amd64 kernel, hostapd 1.0-3+b2

lspci -v:
01:00.0 Network controller: Qualcomm Atheros AR93xx Wireless Network
Adapter (rev 01)
	Subsystem: Qualcomm Atheros Device 3112
	Physical Slot: 0
	Flags: bus master, fast devsel, latency 0, IRQ 16
	Memory at fe9e0000 (64-bit, non-prefetchable) [size=128K]
	Expansion ROM at fe9d0000 [disabled] [size=64K]
	Capabilities: [40] Power Management version 3
	Capabilities: [50] MSI: Enable- Count=1/4 Maskable+ 64bit+
	Capabilities: [70] Express Endpoint, MSI 00
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Virtual Channel
	Capabilities: [300] Device Serial Number 00-00-00-00-00-00-00-00
	Kernel driver in use: ath9k

parts of hostapd.conf that seem relevant: 

interface=wlan0
bridge=br0
driver=nl80211
hw_mode=a
channel=48
rts_threshold=2347
fragm_threshold=2346

wmm_enabled=1
wmm_ac_bk_cwmin=4
wmm_ac_bk_cwmax=10
wmm_ac_bk_aifs=7
wmm_ac_bk_txop_limit=0
wmm_ac_bk_acm=0
wmm_ac_be_aifs=3
wmm_ac_be_cwmin=4
wmm_ac_be_cwmax=10
wmm_ac_be_txop_limit=0
wmm_ac_be_acm=0
wmm_ac_vi_aifs=2
wmm_ac_vi_cwmin=3
wmm_ac_vi_cwmax=4
wmm_ac_vi_txop_limit=94
wmm_ac_vi_acm=0
wmm_ac_vo_aifs=2
wmm_ac_vo_cwmin=2
wmm_ac_vo_cwmax=3
wmm_ac_vo_txop_limit=47
wmm_ac_vo_acm=0

ieee80211n=1
ht_capab=[HT40-][SHORT-GI-40]

wpa=2
wpa_key_mgmt=WPA-PSK WPA-EAP
wpa_pairwise=CCMP TKIP
rsn_pairwise=CCMP