Editing O(1) scheduler (section)

{{Short description|Historical Linux 2.6 kernel process scheduler}}
[[File:Simplified_Structure_of_the_Linux_Kernel.svg|thumb|Location of the "O(1) scheduler" (a [[process scheduler]]) in a simplified structure of the [[Linux kernel]]]]
An '''O(1) scheduler''' (pronounced "O of 1 scheduler", "Big O of 1 scheduler", or "constant time scheduler") is a [[kernel (operating system)|kernel]] [[scheduling (computing)|scheduling]] design that can schedule [[process (computing)|processes]] within a constant amount of time, regardless of how many processes are running on the [[operating system]]. This is an improvement over  previously used [[O(n) scheduler|O(n) schedulers]], which schedule processes in an amount of time that [[Scaling (geometry)|scales]] linearly based on the amounts of inputs.

In the realm of [[real-time operating system]]s, deterministic execution is key, and an O(1) scheduler is able to provide scheduling services with a fixed upper-bound on execution times.

The O(1) scheduler was used in Linux releases 2.6.0 through 2.6.22 (2003-2007), at which point it was superseded by the [[Completely Fair Scheduler]].