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The O(n) scheduler [1] is the scheduler used in the Linux kernel 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 Since version 2.6.0, it has been replaced by the O(1) scheduler and in 2.6.23 by the Completely Fair Scheduler (CFS), which itself was replaced by the current Earliest eligible virtual deadline first (EEVDF) in 6.6.
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 scheduling design that can schedule processes within a constant amount of time, regardless of how many processes are running on the operating system.
A task (i.e., a synonym for thread) is the minimal entity that Linux can schedule. However, it can also manage groups of threads, whole multi-threaded processes, and even all the processes of a given user. This design leads to the concept of schedulable entities, where tasks are grouped and managed by the scheduler as a whole.
The process scheduler is a part of the operating system that decides which process runs at a certain point in time. It usually has the ability to pause a running process, move it to the back of the running queue and start a new process; such a scheduler is known as a preemptive scheduler, otherwise it is a cooperative scheduler. [5]
In February 2003 Andrea Arcangeli put forward his idea for a Stochastic Fair Queueing I/O scheduler to Jens Axboe who then implemented it. Jens Axboe made improvements to his first implementation, calling the new version the Completely Fair Queueing scheduler, and produced a patch to apply it to the 2.5.60 development series kernel.
At any specific time, processes can be grouped into two categories: those that are waiting for input or output (called "I/O bound"), and those that are fully utilizing the CPU ("CPU bound"). In early systems, processes would often "poll" or "busy-wait" while waiting for requested input (such as disk, keyboard or network input). During this time ...
The sleep instruction suspends the calling process for at least the specified number of seconds (the default), minutes, hours or days. sleep for Unix-like systems is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX and the Single Unix Specification. [1] It first appeared in Version 4 ...
Process creation in UNIX and Linux is done through fork() or clone() system calls. There are several steps involved in process creation. The first step is the validation of whether the parent process has sufficient authorization to create a process. Upon successful validation, the parent process is copied almost entirely, with changes only to ...