[ath9k-devel] AR9271-based device regularly loses packets for 18 seconds

[ath9k-devel] AR9271-based device regularly loses packets for 18 seconds

[Alberto Mardegan]

Hi there!
   I bought a Tp-Link TL-WN721N, which appears under lsusb as:

Bus 008 Device 003: ID 0cf3:9271 Atheros Communications, Inc. AR9271 802.11n

The device worked out of the box (kernel version is 3.16.0-38-generic 
#52~14.04.1-Ubuntu), but the connection goes completely silent from time 
to time, for about 18 seconds.

I've kept a long running "ping -D google.com" process, and I've seen 
that every two minutes 17 or 18 ping packets are lost.
I won't attach the whole output of the ping command, I'll just show you 
the last lines *before* the lost packets:

[1432536493.004202] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=829 ttl=53 time=5.55 ms
[...]
[1432536613.152717] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=949 ttl=53 time=2.47 ms
[1432536618.838819] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=954 ttl=53 time=653 ms
[...]
[1432536732.424766] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=1068 ttl=53 time=2.91 ms
[...]
[1432536852.722089] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=1188 ttl=53 time=2.44 ms
[...]
[1432536973.016098] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=1308 ttl=53 time=4.92 ms
[...]
[1432537093.304302] 64 bytes from cache.google.com (87.245.198.34): 
icmp_seq=1428 ttl=53 time=2.28 ms

As you can see, with an exception between rows 2 and 3, all the other 
timestamps differ by 120 seconds, aka two minutes.

Other computers running on the same network don't experience such 
issues, and when I've attached the adaptor to another PC (also running 
Ubuntu 14.04), I've experienced the same problems.

It looks to me that this behaviour is probably triggered by the driver 
of by the firmware. Do you have any idea of what might be causing this?

Is this a known issue?

Ciao,
   Alberto