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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 also known as least laxity first.
EEVDF was first described in the 1995 paper "Earliest Eligible Virtual Deadline First : A Flexible and Accurate Mechanism for Proportional Share Resource Allocation" by Ion Stoica and Hussein Abdel-Wahab. [2] It uses notions of virtual time, eligible time, virtual requests and virtual deadlines for determining scheduling priority. [1]
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.) the queue will be searched for the process closest to its deadline.
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). [1] In periodic real-time task model, a task's processor utilization is defined as execution time over period.
There is no universal best scheduling algorithm, and many operating systems use extended or combinations of the scheduling algorithms above. For example, Windows NT/XP/Vista uses a multilevel feedback queue, a combination of fixed-priority preemptive scheduling, round-robin, and first in, first out algorithms. In this system, threads can ...
A process that is ready to run but waiting for the CPU can be considered blocked. A priority scheduling algorithm can leave some low-priority processes waiting indefinitely. A steady stream of higher-priority processes can prevent a low-priority process from ever getting the CPU. [1]
Fixed-priority preemptive scheduling is a scheduling system commonly used in real-time systems. [1] With fixed priority preemptive scheduling, the scheduler ensures that at any given time, the processor executes the highest priority task of all those tasks that are currently ready to execute.
As part of the scheduling, the processor gives a priority level to different processes running on the machine. When two processes are requesting service at the same time, the processor performs the jobs for the one with the higher priority. There are six named priority levels: Realtime; High; Above Normal; Normal; Below Normal; Low; These ...