Exploring the potential of context-aware dynamic CPU undervolting

CPU operation at sub-nominal voltage levels has been researched to reduce the power and energy consumption of computer systems. While it is possible to determine a safe undervolting level for each application, typically only the most conservative setting is applied statically across all workloads. In this paper, we go a step further and investigate the gains that can be achieved by dynamically and transparently changing the level of CPU undervolting at runtime. To enable this functionality, we design and implement a novel, OS-level, context-aware dynamic undervolting mechanism, able to decide and apply voltage levels according to the specific tolerance of each workload that executes on a multicore CPU at a particular time. Our mechanism can further differentiate between the user- and kernel-level code executed within the same application thread, enabling the exploitation of differences in their undervolting potential. User- and kernel-level code have inherently different characteristics, yet in previous work have never been characterized individually. Our experiments, on an Intel x86-64 multicore show that the proposed approach can reduce the average CPU power consumption by 5.58%/30.05% compared to static undervolting and the nominal voltage level, respectively. Finally, we provide indicative estimates for the gains that could be achieved in future CPU architectures with multiple, per-core voltage domains.