An energy-efficient assignment of a task set T to a group of M processing devices models the process of deciding the assignment as a combinatorial optimization problem having an objective function optimizing the power consumption of the devices when executing subsets of the tasks, under a constraint that the total utilization of the task subset assigned to each respective processing device is lower than a threshold depending on the number of its processor cores. The objective function may be: min Σi=1M Pi(τi), where τi denotes the subset of tasks allocated to the ith device, and Pi(τi) represents power consumption of the ith device when executing τi, and the constraint Uτi≤Mi/4 for all the devices, where Uτi is the total utilization of τi executing on the ith device, and Mi denotes the number of cores of the ith device. Solving the problem using a MaxMin or genetic algorithm gives good energy efficiency.