[ath9k-devel] Atheros Throughput with Aggregation & Encryption

[Mahesh Kumar <mkumar@solectek.com>]

Hello,

We have a critical issue in getting the high throughput, once we enable 
both the Aggregation (AMPDU) and Encryption (WPA) at the same time. (We 
are using the AR9160 chipset.)

Our test setup is like this,

[PC1] ---> [Access Point] --> [Client] --> [PC2].

We are sending a 100 Mbps of UDP traffic from PC1 to PC2. The 
Aggregation (AMPDU) & Encryption are enabled on both "Access point" and 
the "Client". Very low traffic ( < 1Mbps) is reaching at the PC2, that 
also occasionally. Most of the traffic is dropped at the Access point 
itself. When we check the transmit status descriptor@the Access 
point, it shows , lots of "Tx delimiter under-run error" & " Tx data 
under-run error".

Once the driver gets "under-run" error, it starts adjusting the Tx FIFO 
trigger level [TXCFG register, Frame Trigger level], and it finally 
reaches it's maximum. This register specifies the minimum number of 
bytes that must be DMAed  into the PCU TXFIFO, before the PCU initiates 
the frame on the air.

Any idea on why it's happening ?. Are we missing any special kind of 
configuration ?. Or is there any known issue when we enable both 
Aggregation (AMPDU) and encryption simultaneously ?.

The same setup is working, if we disable the Encryption ( getting around 
95.7 Mbps). Also the encryption alone is working, without the 
Aggregation, though we are getting a degraded performance ( max around 
30 Mbps.)
 

Thanks in advance,
Mahesh.