Energy Management

The most important hardware mechanisms which allow software to manage the energy consumption of the parts of the system we are interested in are dynamic voltage and frequency scaling (DVFS) and processor sleep states. Misconceptions about the effect and use of these mechanisms abound, and therefore we will discuss the fundamentals of their use for energy management in Chapter 2.

Virtualization is now firmly entrenched in enterprise computing systems. There are a multitude of reasons for the strong uptake of virtualization in enterprise computing, most having to do with saving cost, and energy. However, virtualization is now also taking hold in the domain of embedded systems. Again, there is a variety of reasons, some similar to the motivations driving uptake in enterprise computing, some different. In Chapter 3 we will give an overview of virtualization, particularly as it relates to embedded systems.

Energy is a global resource, and managing it locally will, in general, not produce optimal results. This means, energy management must be done by, or in cooperation with the software which controls the physical resources of a system. Normally, this is the operating system, but in a virtualized system, it is the hypervisor. Moreover, the hypervisor presents a level of indirection which introduces new degrees of freedom into energy management. We discuss this in Chapter 4.

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