Effectiveness Analysis of DVFS and DPM in Mobile Devices

The demand for high-performance embedded processors in multimedia mobile electronics is growing and their power consumption thus increasingly threatens battery lifetime. It is usually believed that the dynamic voltage and frequency scaling (DVFS) feature saves significant energy by changing the performance levels of processors to match the performance demands of applications on the fly. However, because the energy efficiency of embedded processors is rapidly improving, the effectiveness of DVFS is expected to change. In this paper, we analyze the benefit of DVFS in state-of-the-art mobile embedded platforms in comparison to those in servers or PCs. To obtain a clearer view of the relationship between power and performance, we develop a measurement methodology that can synchronize time series for power consumption with those for processor utilization. The results show that DVFS hardly improves the energy efficiency of mobile multimedia electronics, and can even significantly worsen energy efficiency and performance in some cases. According to this observation, we suggest that power management for mobile electronics should concentrate on adaptive and intelligent power management for peripheral devices. As a preliminary design, we implement an adaptive network interface card (NIC) speed control that reduces power consumption by 10% when NIC is not heavily used. Our results provide valuable insights into the design of power management schemes for future mobile embedded systems.