Mobile devices including phones, tablets, and labtops rely on batteries, whose capacity is limited. Thus, power management has become very significant. However, the performance, especially response latency to user inputs, still matters and the response latency is often the most significant factor for the first user experiences; e.g., at stores or during demonstrations. In order to address response latency, we integrate PM-QoS framework with DVFS frameworks (CPUfreq and devfreq). DVFS is very effective on reducing power consumption with minimal performance deterioration. However, when we focus on the response latency, not average throughput, DVFS deteriorates the latency significantly. We show how QoS/DVFS can be modified (including what we are upstreaming) and integrated and how to use them to improve the performance of your Linux mobile devices for kernel and device driver developers.