Online power management using DVFS for RTOS

Power management is essential in microprocessor-based system design to avoid heat dissipation and preserve battery life time. In mobile devices running real time applications, the power consumed by the CPU can be more than the needed amount of power for best performance. At first glance, one can think of reducing the power budget of the system. Although this may seem an appealing easy solution, it can cause a huge degradation in performance if not controlled properly. Also a real time application's requirements vary with time, which implies that the power budget should also be variable. There must be a trade-off between power management and performance such that, the power consumed is always proportional to the required performance level. DVFS (dynamic voltage and frequency scaling) can be used to change the operating point (voltage-frequency pair) of the CPU according to the application's power requirement. In this paper, we present an implementation of a negative feedback control algorithm that uses DVFS for power saving in soft real-time systems that runs on Mentor Graphics^® Nucleus^® RTOS. A monitor periodically calculates the CPU utilization in runtime and reports it to the controller which adjusts the CPU operating point online such that the best performance is achieved with least power consumption. Our experimental results show that power savings up to 24% can be achieved just by using the proposed DVFS on a platform that supports only frequency scaling.