The push for energy-efficient and energy-proportional computing nodes, together with the increasing number of cores integrated in the same silicon die has lead to computing nodes with fine grained power management capabilities. To unleash the potential of this HW design a novel user-space power management APIs is needed to bring fine-grain power management in the hands of the programmer. In this work we present a novel programming mechanism for energy efficiency which is build around novel user-space power management APIs suitable to be embedded in user-space applications. We evaluated its timing and power saving performance on a novel computing node based on Cavium ThunderX ARMv8-based many-cores SoC.