Dynamic priority scheduling is a type of
scheduling algorithm
In computing, scheduling is the action of assigning ''resources'' to perform ''tasks''. The ''resources'' may be processors, network links or expansion cards. The ''tasks'' may be threads, processes or data flows.
The scheduling activity is ca ...
in which the priorities are calculated during the execution of the system. The goal of dynamic priority scheduling is to adapt to dynamically changing progress and to form an optimal configuration in a self-sustained manner. It can be very hard to produce well-defined policies to achieve the goal depending on the difficulty of a given problem.
Earliest deadline first scheduling
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) ...
and
Least slack time scheduling
Least slack time (LST) scheduling is an algorithm for dynamic priority scheduling. It assigns priorities to processes based on their ''slack time''. Slack time is the amount of time left after a job if the job was started now. This algorithm is al ...
are examples of Dynamic priority scheduling algorithms.
Optimal Schedulable Utilization
The idea of real-time scheduling is to confine processor utilization under schedulable utilization of a certain scheduling algorithm, which is scaled from 0 to 1. Higher schedulable utilization means higher utilization of resource and the better the algorithm. In preemptible scheduling, dynamic priority scheduling such as
earliest deadline first (EDF) provides the optimal schedulable utilization of 1 in contrast to less than 0.69 with fixed priority scheduling such as
rate-monotonic (RM).
[Krishna, C.M. and Shin, K.G. Real-time Systems, , 1997]
In periodic real-time task model, a task's processor utilization is defined as execution time over period. Every set of periodic tasks with total processor utilization less or equal to the schedulable utilization of an algorithm can be feasibly scheduled by that algorithm. Unlike fixed priority, dynamic priority scheduling could dynamically prioritize task deadlines achieving optimal schedulable utilization in the preemptible case.
See also
*
Earliest deadline first scheduling
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) ...
*
Least slack time scheduling
Least slack time (LST) scheduling is an algorithm for dynamic priority scheduling. It assigns priorities to processes based on their ''slack time''. Slack time is the amount of time left after a job if the job was started now. This algorithm is al ...
References
Scheduling algorithms
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