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The scheduler is an operating system module that selects the next jobs to be admitted into the system and the next process to run. Operating systems may feature up to three distinct scheduler types: a long-term scheduler (also known as an admission scheduler or high-level scheduler), a mid-term or medium-term scheduler, and a short-term scheduler.
Scheduling zoo (by Christoph Dürr, Sigrid Knust, Damien Prot, Óscar C. Vásquez): an online tool for searching an optimal scheduling problem using the notation. Complexity results for scheduling problems (by Peter Brucker, Sigrid Knust): a classification of optimal scheduling problems by what is known on their runtime complexity.
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.
It uses notions of virtual time, eligible time, virtual requests and virtual deadlines for determining scheduling priority. [1] It has the property that when a job keeps requesting service, the amount of service obtained is always within the maximum quantum size of what it is entitled.
The criteria of a real-time can be classified as hard, firm or soft.The scheduler set the algorithms for executing tasks according to a specified order. [4] There are multiple mathematical models to represent a scheduling System, most implementations of real-time scheduling algorithm are modeled for the implementation of uniprocessors or multiprocessors configurations.
Generalized Foreground-Background (FB), also known as Least Attained Service (LAS) is a scheduling policy. [1] It consists in scheduling the process that has received the least service so far. Similarly to SRPT, the aim of FB is to improve the performance of a system, specifically mean response time. While SRPT is optimal it is more difficult ...
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.
An equivalent problem is scheduling when machines are available in different times: each machine i becomes available at some time t i ≥ 0 (the time t i can be thought of as the length of the kernel job). A simple heuristic algorithm, called SLPT, [23] assigns each kernel to a different subset, and then runs the LPT algorithm.