Energy-conserving feedback EDF scheduling for embedded systems with real-time constraints

Embedded systems have limited energy resources. Hence, they should conserve these resources to extend their period of operation. Recently, dynamic frequency scaling (DFS) and dynamic voltage scaling (DVS) have been added to a various embedded processors as a means to increase battery life. A number of scheduling techniques have been developed to exploit DFS and DVS for real-time systems to reduce energy consumption. These techniques exploit idle and slack time of a schedule. Idle time can be consumed by lowering the processor frequency of selected tasks while slack time allows later tasks to execute at lower frequencies with reduced voltage demands.Our work delivers energy savings beyond the level of prior work. We enhance the earliest-deadline first (EDF) scheduling to exploit slack time generated by the invocation of the task at multiple frequency levels within the same invocation. The technique relies strictly on operating system support within the scheduler to implement the approach. Early scaling at a low frequency, determined by a feedback mechanism and facilitated by a slack-passing scheme, capitalizes on high probabilities of a task to finish its execution without utilizing its worst-case execution budget. If a task does not complete at a certain point in time within its low frequency range, the remainder of it continues to execute at a higher frequency. Our experiments demonstrate that the resulting energy savings exceed those of previously published work by up to 33%. In addition, our method only adds a constant complexity at each scheduling point, which has not been achieved by prior work, to the best of our knowledge.