A method and associated systems for using a software-defined network (SDN) controller to automatically test cloud performance. A bandwidth measuring and optimizing system associated with the SDN controller detects a triggering condition and, in response, directs a network-management tool to measure a bandwidth of a segment of a physical infrastructure of a network and directs the SDN controller to provision a virtual machine that then measures a bandwidth of a corresponding segment of virtual infrastructure that is overlaid upon the physical segment. In some embodiments, these two tests are synchronized so as to concurrently measure physical and virtual bandwidths while the same test data passes through the virtual infrastructure segment. The measured bandwidth of the virtual segment is then compared to the measured bandwidth of the physical segment in order to determine an efficiency of the virtual network.