SDIO Performance once again

[Dominik S. Herwald]

Hello,

right now I am testing Marvell 8686 based Modules connected to the SDIO
Controller of a Blackfin BF548.

Basically the libertas driver works just fine and stable.  
But the Performance... :-/ 


# iperf -c 192.168.10.11 -i 1 -w 208K    
------------------------------------------------------------
Client connecting to 192.168.10.11, TCP port 5001
TCP window size:   208 KByte
------------------------------------------------------------
[  5] local 192.168.10.23 port 45592 connected with 192.168.10.11 port 5001
[  5]  0.0- 1.0 sec    488 KBytes  4.00 Mbits/sec
[  5]  1.0- 2.0 sec    320 KBytes  2.62 Mbits/sec
[  5]  2.0- 3.0 sec    376 KBytes  3.08 Mbits/sec
[  5]  3.0- 4.0 sec    320 KBytes  2.62 Mbits/sec
[  5]  4.0- 5.0 sec    376 KBytes  3.08 Mbits/sec
[  5]  5.0- 6.0 sec    376 KBytes  3.08 Mbits/sec
[  5]  6.0- 7.0 sec    320 KBytes  2.62 Mbits/sec
[  5]  7.0- 8.0 sec    368 KBytes  3.01 Mbits/sec
[  5]  8.0- 9.0 sec    320 KBytes  2.62 Mbits/sec
[  5]  9.0-10.0 sec    376 KBytes  3.08 Mbits/sec
[  5]  0.0-10.1 sec  3.56 MBytes  2.95 Mbits/sec


If I reduce the TCP Window size to 16K it hits either
2.62 or 2.69MBit/s all the time.

Both 8686 Modules show identical behaviour with different Antennas so I 
can rule out
a Hardware issue.

iwconfig says
Bit Rate 54Mbit/s,  100/100 Link Quality,  Signal Level -17dBm, Noise 
Level -93dBm
The WLAN AP is 50cm away on the same table.
CPU Load is only around 3%. Top and iperf are running in two telnet 
sessions over WLAN
and it doesn't matter if WPA or WEP Encryption is used...



############

It does not matter what I change, be it the SDIO Clock (12MHz or 22MHz - 
does not matter)
or 1 Bit SDIO (with IRQ) or 4 Bit SDIO (without IRQ).

Looking at the SDIO Signals with a Scope, I see big ~3ms Gaps between 
all the
transfers while running iperf.
Each transfer is around 1ms long at SDIO Clock of about 12MHz
These Gaps/Delays between transfers are always there - also if just top 
is running
in a telnet session.

I am no SDIO expert, but is this normal?

############



Is the 8686 the limiting factor, or the Firmware
(I tried both, the 8.73 and 9.7 from Marvell)
or the libertas driver or the SDIO Controller?

Any ideas how to improve it?


Best regards,
Dominik