The Power of Isolation

Non-functional system properties such as CPU and memory utilization as well as power consumption are usually non-compositional. However, such properties can be made compositional by isolating individual system components through over-provisioning. The challenge is to relate the involved isolation cost and the resulting isolation quality properly. Temporal and spatial isolation have been studied extensively. Here we study the compositionality of power consumption as another and in this regard unexplored example of a non-linear property with many important applications. In particular, we introduce the concept of power isolation for EDF-scheduled hard real-time systems running periodic software tasks. A task is power isolated if there exist lower and upper bounds on its power consumption independent of any other concurrently running tasks. The main challenges in providing power isolation are to find a relationship between the power consumption of a system and the contribution of a single task to this power consumption as well as understanding the trade-off between quality and cost of power isolation. We present lower and upper bounds on the power consumption of a task as functions of task utilization, frequency scaling, and power model. Furthermore, we discuss the variance between lower and upper bounds (quality) and the power consumption overhead (cost) of power isolation.