Impact of operating points on DVFS power management

Dynamic voltage and frequency scaling (DVFS) techniques are commonly used for energy management in modern systems to reduce processor clock frequency and corresponding voltages. This reduces overall power and energy utilization. However the power levels associated with corresponding frequencies play an important role in effective DVFS based strategies, as in some cases energy utilization can actually be increased. We present a DVFS based power strategy dedicated to video processing with an application to an H.264 decoder. We analyze the effectiveness of this strategy using an ARM1176JZF-S hardware platform and a QEMU based virtual platform configured with models of ARM processors. Our results show that we can gain up to 57 % by choosing correct adaptation constraints. However, results also show that the efficiency of a DVFS strategy depends upon the characteristics of operating points (frequency/voltage couples). In particular, attention must be paid to the power level gap between consecutive frequencies, to compensate the increase in execution time resulting from frequency downscaling*.