Off-the-shelf embedded systems have adopted heterogeneous multi-core processors which have high-performance big cores and low-power small cores. Though there are two different types of cores in heterogeneous multi-core processors, conventional DVFS (Dynamic Voltage and Frequency Scaling)-based DTM (Dynamic Thermal Management) techniques do not utilize the different types of cores to cool down hot cores. Rather, they primarily reduce the voltage and frequency of the hot cores, leading to performance degradation. In this article, we propose a novel adaptive DTM framework for heterogeneous multi-core processors, which utilizes the big and small cores to prevent performance degradation. Our proposed framework exploits two migration-based DTM techniques: 1) a technique (denoted as Migrationbig↔big) that migrates applications from hot big cores (big cores whose temperature is above a pre-defined threshold) to cold big cores (big cores whose temperature is below the threshold) and 2) a technique (denoted as Migrationbig↔small) that migrates all applications from the big cores to the small cores. In case of thermal emergency of the big cores, our proposed framework checks the number of cold big cores. When there exist available cold big cores, our proposed framework employs Migrationbig↔big to cool down the hot big cores while not reducing the big core frequency. On the other hand, when there does not exist any available cold big core, our proposed framework employs one between Migrationbig↔small and a DVFS-based DTM technique, which is expected to result in better performance. In our experiments on an embedded development board, our proposed framework improves the average performance by 8.9 percent, compared to ARM's DVFS-based IPA (Intelligent Power Allocation), satisfying thermal constraints. Our framework also improves the average performance by 10.4 percent, compared to a state-of-the-art predictive DVFS-based DTM technique.

Recent smart devices have adopted heterogeneous multi-core processors which have high-performance big cores and low-power small cores. Unfortunately, the conventional task scheduler for heterogeneous multi-core processors does not provide appropriate amount of CPU resources for multimedia applications (whose QoS is important to users), resulting in energy waste; it often executes multimedia applications and non-multimedia applications on the same core. In this paper, we propose an advanced task scheduler for heterogeneous multi-core processors, which provides appropriate amount of CPU resources for multimedia applications. Our proposed task scheduler isolates multimedia applications from non-multimedia applications at runtime, exploiting the fact that multimedia applications have a specific thread for video/audio playback (to play video/audio, a multimedia application should use a function that generates the specific thread). Since multimedia applications usually require a smaller amount of CPU resources than non-multimedia applications due to dedicated hardware decoders, our proposed task scheduler allocates the former to the small cores and the latter to the big cores. In our experiments on an Android-based development board, our proposed task scheduler saves system-wide (not just CPU) energy consumption by 8.9 percent, on average, compared to the conventional task scheduler, preserving QoS of multimedia applications. In addition, it improves performance of non-multimedia applications by 13.7 percent, on average, compared to the conventional task scheduler.