The controller is running as a master and currently serving only 3 APs (AP-105, AP-134, AP-135).
I start Iperf with the options "-s -w 512K -i 1" on a machine running Windows 8 or a Macbook with OS X 10.10, both directly connected to the controller.
On the controller I used the following command: perf-test client start controller host x.x.x.x tcp window 512K