In a method of operating a multi-core system comprising a plurality of processor cores, a plurality of task stall information respectively corresponding to a plurality of tasks are provided by monitoring a task stall time with respect to each task. The task stall time indicates a time while the each task is suspended within a task active time, and the task active time indicates a time while a corresponding processor core is occupied by the each task. Task scheduling is performed based on the plurality of task stall information, and a fine-grained dynamic voltage and frequency scaling (DVFS) is performed based on the task scheduling. The plurality of tasks may be assigned to the plurality of processor cores based on load unbalancing, and the effects of the fine-grained DVFS may be increased to reduce the power consumption of the multi-core system.