QScale: Thermally-efficient QoS management on heterogeneous mobile platforms

Single-ISA heterogeneous mobile processors integrate low-power and power-hungry CPU cores together to combine energy efficiency with high performance. While running computationally demanding applications, current power management and scheduling techniques greedily maximize quality-of-service (QoS) within thermal constraints using power-hungry cores. We show that such an approach delivers short bursts of high QoS, but also causes severe QoS loss over time due to thermal throttling. To provide mobile users with sustainable QoS over extended durations, this paper proposes QScale. QScale is a novel thermally-efficient QoS management framework for mobile devices with heterogeneous multi-core CPUs. QScale leverages two novel observations to provide thermally-efficient QoS: (1) threads of a mobile application exhibit significant heterogeneity, which can be exploited during scheduling; (2) thermal efficiency of core allocation decisions is significantly altered by thermal interactions across system-on-a-chip (SoC) components and application characteristics. QScale coordinates closed-loop frequency control with thermally-efficient scheduling to deliver the desired QoS with minimal exhaustion of processor thermal headroom. Our experiments on a state-of-the-art heterogeneous mobile platform show that QScale meets target QoS levels while minimizing heating, achieving up to 8× longer durations of sustainable QoS.