Trouble shooting low rate MCS9 in 802.11ac

[Vu Hai NGUYEN]

>>>So probably the air condition you have forces the rate control to pick
>>>MCS7 as the most suitable rates.

>> What could I do to improve this? (Change the air conditioner LOL?)

>Heh, he meant the RF environment in the location you are. :)
>And ugh - this is why we need an open source ART already.

My 2 devices have an ARM processor 1200MHz.
If I connect these two devices by an Ethernet cable and doing iperf (in TCP)
I can obtain 880 Mbps, it means that my processor can deal with that speed 
of data transfer. But if I use Wi-fi instead of Ethernet to test rate between these
devices, my processor is exhausted, I run command top and see that 0~1% 
idle only,  ksoftirqd and kworker take most of my processor resource. 

Last week I discovered by chance that the module loaded in kernel can create 
effects to performance of rate, in my case it is "iptables". If I unload all module 
that related to iptables I can improve the performance. 
So I wonder if I can do some thing with the Wi-fi driver to  improve rate? 
Or the only solution is overclock/change my processor?

NGUYEN Vu Hai
Acita-Sodielec
Route de Mayres - B.P. 9
12100 St GEORGES DE LUZENCON
FRANCE