Figure 1 gives an overview of the RightSpeed design. Applications convey information about their tasks to the operating system using system calls. This information includes when tasks begin and end and what performance targets the application wants for those tasks. Some applications are oblivious to the existence of these system calls, so an automatic task detector infers task information about them and generates task specification system calls on their behalf. The system uses information about ongoing tasks to determine what speed to use at various times, and implements this schedule using timers and special processor instructions that change speed and voltage. The system uses a PACE calculator to compute the most energy efficient schedules that have the performance requested.
In addition to the above functionality, we had three overall goals for RightSpeed. First, we wanted it to be efficient, creating low overhead on the system both when running in the background and when actively invoked. Second, we wanted it to be stable, relying only on documented system interfaces so that it would run even when the operating system was upgraded. Third, we wanted it to be easily portable to different processors despite such processors having different commands dealing with speed and voltage settings.
