Power management based on policy

A machine's power usage may be managed by a power-management policy. When a program makes a request that involves use of one of the machine's power-consuming devices, the policy may take into account factors such as the program's status, where the status indicates the program's relative level of justification to consume power. A component may intercept a request to use a device before the request reaches the driver, and may deflect requests that, if carried out, are not consistent with power usage policy. Infrastructure supports the use of policies that determine whether a particular device's power state will be changed.