1. A data processing device, comprising: a processor operable at selectable ones of a plurality of performance levels and configured to provide for supply of workload data indicating a workload of the processor as a function of time; a pattern memory, for storing control information to control performance level in combination with a plurality of reference workload data vectors, each reference workload data vector containing workload data for a series of successive sampling periods; a pattern matcher configured to detect for a current sampling period whether there is a matching workload data vector from the plurality of reference workload data vectors that matches a current workload data vector of workload data of the processor during a series of preceding sampling periods preceding the current sampling period; a performance level controller, configured to select the performance level of the processor, based on the control information that is stored in combination with the matching workload data vector.