Hardware Reference
In-Depth Information
Task control block A kernel data structure associated with each task containing all
the information necessary for task management.
Temporal Isolation A kernel mechanism able to enforce resource reservation on
the processor, so that the tasks running within the reservation are guaranteed to
receive the reserved amount of time and do not interfere on the others for more
than the reserved amount. Temporal isolation allows each task to behave as it were
executing alone on a slower processor with speed equal to the reserved fraction.
Task protection
A synonym of Temporal Isolation.
Tick The minimum interval of time that is handled by the kernel. It defines the time
resolution and the time unit of the system.
Timeout
The time limit specified by a programmer for the completion of an action.
Time-overflow Deadline miss. A situation in which the execution of a job continues
after its deadline.
Timesharing A kernel mechanism in which the available time of the processor is
divided among all active jobs in time slices of the same length.
Time slice A continuous interval of time in which a job is executed on the processor
without interruption.
Utilization factor The fraction of the processor time utilized by a periodic compu-
tation. The utilization factor of a periodic task τ i is the ratio of its computation time
and its period ( U i = C i /T i ). The utilization factor of a periodic task set is the sum
of the individual task utilizations ( U = i U i ).
Utility function
A curve that describes the value of a task as a function of its finish-
ing time.
Value A task parameter that describes the relative importance of a task with respect
to the other tasks in the system.
Value Density
The ratio between the value of a task and its computation time.
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