1. For a controller, a method for controlling a logical switching element comprising one or more logical ports, the logical switching element implemented in one or more managed switching elements that forward data in a network, each managed switching element having one or more ports to which machines connect, the method comprising: receiving user inputs for specifying (i) a logical queue for a logical port of the logical switching element for implementing a logical data path set (LDPS) and (ii) a set of performance constraints to apply to the logical port using the logical queue; based on the user inputs, creating the logical queue for the logical port and applying the set of performance constraints to the logical port, wherein the logical port is mapped to a particular port of a managed switching element to which a particular machine connects; and associating the logical queue with a physical queue for the particular port of the managed switching element, the physical queue for queuing data received at the managed switching element through the particular port according to the set of performance constraints before the managed switching element sends the data toward a destination of the data.