This is my network topology:
To exclude Interference between antennas I replicated the same experiments with two soekris instead of one.
Specifically, I use the same antenna placement but I sobstituted the second wireless card of B with
another dedicated soekris
In this scenario I achieved a per flow throughput of about 24-25 Mbps. So there isn't interference between antennas.
To excluded interference between wireless cards I repeated the same experiment of the first scenario using a PC equipped with
an Athlon 64 processor (2043.086 MHz processor with 1GB of memory). I put both the wireless cards into two contiguous PCI slots
using two miniPCI to PCI single Slot Adapter so that the wireless cards are about 1-2 cm from each other. Also in this case
both the wireless cards are able to work simultaneously and I obtained a per flow throughput of about 24-25Mbps.
I also opened the case of the soekris B and D of the second scenario and I bring the wireless card of soekris B near to the wireless card of soekris D
(varying their relative position ). Also in this case I obtained a per flow throughput of about 24-25Mbps.
This is a snapshot of the CPU utilization obtained with the top command when both wireless cards work simultaneously:
Cpu(s): 4.2%us, 27.8%sy, 0.0%ni, 0.0%id, 0.0%wa, 15.2%hi, 52.8%si, 0.0%st
As you can observe, the amount of time the CPU has been servicing software interrupts is about 52.8%,
and the total CPU utilization is about 100%.
When I only use one wireless cards, the output of the top command is very similar to that obtained with two wireless card
Specifically, the %si field is about 50%, and the total CPU usage is about 100%.
It's very strange that also with one wireless card and one asimptotic UDP flow the %si filed is about 50%.
Consequently, I think that the problem is related to the madwifi driver or to the soekris board.
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