Exploiting big.LITTLE Batteries for Software Defined Management on Mobile Devices

Battery service time is a critical constraint on the availability and functionality of mobile devices. Equipping larger batteries may mitigate such deficiency yet it raises the challenges on thermal limit and physical size. Changing the battery chemistry is another solution, which however usually benefits the energy efficiency of only part of the applications, depending on their software behaviors. To address the challenges of battery energy efficiency and heat dissipation in limited physical space, we propose CAPMAN, a management framework that jointly optimizes the
c
ooling and
a
ctive
p
ower
man
agement in a smartphone, a typical mobile device, equipped with a hybrid battery pack. We establish the framework with three components. First, we abstract the correlation among the batteries, devices and software into a finite state machine model, whose state transitions can be triggered by actions like system calls and user activities. Second, we propose a battery scheduling algorithm that determines the more suitable battery for cooling/active power use, with respect to the dynamic software behaviors and their impact on the hardware states, based on a Markov decision process (MDP). Third, we design a facility for joint cooling and active power management by coordinating TECs and batteries. With the three major designs, CAPMAN realizes software defined management that schedules heterogeneous batteries and TEC cooling in a timely manner. In addition, CAPMAN provides an online algorithm with a proved O(1.05)-competitiveness performance. With a pair of big.LITTLE batteries, we prototype CAPMAN on multiple popular smartphones and a PYNQ development board. The evaluation with real-world workloads shows that compared to the current mainstream, CAPMAN can achieve 114 percent longer battery service time under skewed loads; compared to the state-of-the-practice baselines, CAPMAN shows 55 percent performance gain and 53 percent less energy use on average. Those results approve that big.LITTLE batteries with sophisticated software defined management is an effective way to prolong the battery service times on mobile devices.