Aggressive Voltage and Temperature Control for Power Saving in Mobile Application Processors

DVFS is a widely used methodology for reducing the power consumption of mobile devices. This scheme involves frequency scaling in accordance with a specific governor and the establishment of an operating voltage to be paired with frequency. Incorporated into the settings for operating voltage is a guardband that ensures safe processor operation even at the worst conditions of on-chip temperature. Typically, the processor temperature remains at a normal range (i.e., not the worst), hence the voltage guardband set to guarantee safe operation is overly protected. In this paper, we propose a temperature-aware DVS (T-DVS) that aggressively reduces voltage guardband. We explore the opportunity to provide minimum operating voltages for frequencies at different temperatures and realize a dynamic voltage control scheme that reduces power consumption. The T-DVS manages temperature so that it remains in the 'green zone' where maximum voltage gain is enabled for power-efficient operation. We validate the effectiveness of the T-DVS under various thermal conditions by using mobile application processors and different operating scenarios. Experimental results show that the T-DVS leads to power gain without degrading performance regardless of thermal conditions and chip characteristics. By examining the real-world applications of and off-the-shelf smartphone, we show that the voltage gains generated by the T-DVS results in battery lifetime increment.