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The O(n) scheduler is the
The O(n) scheduler is the scheduler
A schedule (, ) or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such things ...
used in the Linux kernel
The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...
between versions 2.4 and 2.6. Since version 2.6.0, it has been replaced by the O(1) scheduler and in 2.6.23 by the Completely Fair Scheduler
The Completely Fair Scheduler (CFS) was a process scheduler that was merged into the 2.6.23 (October 2007) release of the Linux Linux kernel, kernel. It was the default scheduler of the tasks of the SCHED_NORMAL class (i.e., tasks that have no re ...
(CFS), which itself was replaced by the current Earliest eligible virtual deadline first (EEVDF) in 6.6.
Algorithm
This scheduler divides processor time into epochs. Within each epoch, every task can execute up to its time slice. If a task does not use all of its time slice, then the scheduler adds half of the remaining time slice to allow it to execute longer in the next epoch.Advantages
This scheduler was better in comparison to the previously used very simple scheduler based on a circular queue.Disadvantages
If the number of processes is big, the scheduler may use a notable amount of the processor time itself. Picking the next task to run requires iteration through all currently planned tasks, so the scheduler runs in O(n) time, where n is the number of the planned processes.See also
References