Editing O(1) scheduler (section)

== Overview ==
The Linux scheduler was overhauled completely with the release of kernel 2.6 in 2003.<ref>{{Cite web|url=https://www.linuxjournal.com/article/6530|title=Introducing the 2.6 Kernel {{!}} Linux Journal|website=www.linuxjournal.com|access-date=2019-07-19}}</ref><ref>{{cite web|url=http://www.linuxjournal.com/magazine/completely-fair-scheduler|title=Completely Fair Scheduler|author=Chandandeep Singh Pabla|date=August 1, 2009|website=linux journal|access-date=2014-09-09}}</ref> The new scheduler was called the O(1) scheduler. The algorithm used by the O(1) scheduler relies on active and expired arrays of processes to achieve constant scheduling time. Each process is given a fixed time quantum, after which it is [[preemption (computing)|preempted]] and moved to the expired array. Once all the tasks from the active array have exhausted their time quantum and have been moved to the expired array, an array switch takes place. Because the arrays are accessed only via pointer, switching them is as fast as swapping two pointers.<ref>{{cite web
|author = Robert Love
|url = http://www.informit.com/articles/article.aspx?p=101760&seqNum=2
|title = The Linux Process Scheduler
|access-date = 2014-09-09
}}</ref> This switch makes the active array the new empty expired array, while the expired array becomes the active array.