For real-time computer-controlled systems, control performances of tasks as well as energy consumption of overall system must be optimized. A control task does not have a fixed period but a range of periods in which control performance varies. Hence when more than one control tasks are scheduled on a single processor, an optimization problem appears. Furthermore, when an energy saving technique such as dynamic voltage scaling is used, its properties affect the control performance. Using a performance index that involves control performance and energy consumption, a static solution is proposed to obtain optimal processor speed and a set of periods for given control tasks in O(k). Also, a dynamic solution is proposed to utilize system services of real-time operating systems to overcome unavoidable deficiencies of the static solution and to further reduce the energy consumption of the overall system. The performances of proposed solutions are revealed via simulation studies.