Gaming on mobile platforms is highly power hungry and rapidly drains the limited-capacity battery. In multi-threaded gaming, each thread has different processing requirements and even a single slow thread may lead to Quality of Service (QoS) violations. Further, modern mobile platforms are equipped with asymmetric multi-core processors, so that different cores exhibit diverse power and performance properties. These asymmetric cores along with different Dynamic Power Management (DPM) techniques enable a high degree of power efficiency in mobile gaming. The default Linux power manager (i.e. 'Governor') of asymmetric multi-cores performs power-wise inefficient for mobile games as it over allocates resources for processing threads by being oblivious to the QoS. The state-of-the-art Governor for mobile gaming does not account for multi-threaded gaming workloads, which are mainstream in mobile gaming. In this work, we present a power-performance characterization of multi-threaded mobile games by executing them on a real-world mobile platform with an asymmetric multi-core. This analysis is leveraged to propose a QoS-aware Governor running a lightweight online heuristic that holistically accounts for thread-to-core mapping and DPM. This solution, when integrated into the platform's Operating System (OS), provides 12% improved power efficiency on average.