8. Processor Configuration and Control¶
This section describes the configuration and control of the processor’s power and performance states. The major controls over the processors are:
Processor power states: C0, C1, C2, C3, … Cn
Processor clock throttling
Processor performance states: P0, P1, … Pn
These controls are used in combination by OSPM to achieve the desired balance of the following sometimes conflicting goals:
Power consumption and battery life
Because the goals interact with each other, the operating software needs to implement a policy as to when and where tradeoffs between the goals are to be made (see note below). For example the operating software would determine when the audible noise of the fan is undesirable and would trade off that requirement for lower thermal requirements, which can lead to lower processing performance. Each processor configuration and control interface is discussed in the following sections along with how controls interacts with the various goals.
A thermal warning leaves room for operating system tradeoffs (to start the fan or reduce performance), without issuing a critical thermal alert.