Task specification interface

A key piece of information an application must specify about a task is its type. An application may define types any way it chooses; there are two reasons applications will want to classify different tasks into different types. First, it may want to specify different performance targets for different types of tasks. For example, an MPEG player may require a faster speed for processing its I-frames than its smaller P-frames. As another example, it may want a short and hard deadline for its frame playback tasks but a longer and soft deadline for its user interface tasks. Second, tasks of different types may have different CPU requirement distributions, so it is helpful to direct PACE to only consider tasks of the same type when estimating the probability distribution of a task's CPU requirement.

RightSpeed uses this notion of task type to simplify its communication with applications. When an application begins a task, it need only tell RightSpeed the type of that task. RightSpeed can figure out all other information about the task, such as its performance requirements, from that type. RightSpeed can give the application a unique identifier to identify this task, so the application can specify when the task completes by merely passing RightSpeed that identifier. RightSpeed can then determine how many CPU cycles that task used and use this datum to compute a new optimal PACE schedule for the next task of that type.

An application specifies performance targets for task types via a separate part of the task specification interface. An application need only specify this data once, when it is installed. Because task type data is persistent, i.e., it is retained even when the application terminates and even when the system shuts down, a logical abstraction to use for this data is a file. Thus, applications create files containing data for their task types.

An application may specify a performance target in two ways. First, it may specify a number of CPU cycles to be completed by a certain deadline. Second, it may specify a deadline and a particular DVS algorithm, such as Transmeta's LongRun $^{\text {TM}}$, and dictate that performance be the same as would be achieved via that algorithm.