Just enough is more: Achieving sustainable performance in mobile devices under thermal limitations

With the integration of high-performance multicore processors and multiple accelerators into modern mobile system-on-chips (SoCs), power densities have grown substantially. As a result, thermal management policies, which ensure operation at thermally safe conditions, became essential components of state-of-the-art mobile systems. Traditional thermal throttling approaches aim at maximum utilization of the available thermal headroom to minimize the performance loss and maximize user performance. This paper demonstrates that, in a mobile platform, such greedy techniques can lead to significant degradation in the quality-of-service (QoS) levels as the duration of device activity increases, leading to inconsistent user experience over time. We demonstrate that incorporating user/application QoS requirements into mobile power management to provide “just enough” performance (instead of always maximizing performance) allows for more efficient usage of the thermal headroom, which translates to substantially extended durations of sustainable performance. We propose a closed-loop QoS control policy, including an efficient dynamic voltage and frequency scaling (DVFS) state scheduling technique, to minimize the thermal impact for extending the sustainability of desired QoS levels. Experiments on a modern smartphone show that the proposed technique provides up to 74% longer sustainable performance while meeting the target QoS demands for a variety of real-life applications.