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O(n) Scheduler
The O(n) scheduler 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 Since version 2.6.0, it has been replaced by the O(1) scheduler and in 2.6.23 by the current Completely Fair Scheduler The Completely Fair Scheduler (CFS) is a process scheduler that was merged into the 2.6.23 (October 2007) release of the Linux kernel and is the default scheduler of the tasks of the SCHED_NORMAL class (i.e., tasks that have no real-time execution ... (CFS). 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 itse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Simplified Structure Of The Linux Kernel
Simplification, Simplify, or Simplified may refer to: Mathematics Simplification is the process of replacing a mathematical expression by an equivalent one, that is simpler (usually shorter), for example * Simplification of algebraic expressions, in computer algebra * Simplification of boolean expressions i.e. logic optimization * Simplification by conjunction elimination in inference in logic yields a simpler, but generally non-equivalent formula * Simplification of fractions Science * Approximations simplify a more detailed or difficult to use process or model Linguistics * Simplification of Chinese characters * Simplified English (other) * Text simplification Music * Simplified (band), a 2002 rock band from Charlotte, North Carolina * ''Simplified'' (album), a 2005 album by Simply Red * "Simplify", a 2008 song by Sanguine * "Simplify", a 2018 song by Young the Giant from ''Mirror Master'' See also * Muntzing (simplification of electric circuits) * Reduction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheduling (computing)
In computing, scheduling is the action of assigning ''resources'' to perform ''tasks''. The ''resources'' may be processors, network links or expansion cards. The ''tasks'' may be threads, processes or data flows. The scheduling activity is carried out by a process called scheduler. Schedulers are often designed so as to keep all computer resources busy (as in load balancing), allow multiple users to share system resources effectively, or to achieve a target quality-of-service. Scheduling is fundamental to computation itself, and an intrinsic part of the execution model of a computer system; the concept of scheduling makes it possible to have computer multitasking with a single central processing unit (CPU). Goals A scheduler may aim at one or more goals, for example: * maximizing '' throughput'' (the total amount of work completed per time unit); * minimizing ''wait time'' (time from work becoming ready until the first point it begins execution); * minimizing '' latenc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linux Kernel
The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU operating system, which was written to be a free (libre) replacement for Unix. Linux is provided under the GNU General Public License version 2 only, but it contains files under other compatible licenses. Since the late 1990s, it has been included as part of a large number of operating system distributions, many of which are commonly also called Linux. Linux is deployed on a wide variety of computing systems, such as embedded devices, mobile devices (including its use in the Android operating system), personal computers, servers, mainframes, and supercomputers. It can be tailored for specific architectures and for several usage scenarios using a family of simple commands (that is, without the need of manually editing its source c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
O(1) Scheduler
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. This is an improvement over previously used O(n) schedulers, which schedule processes in an amount of time that scales linearly based on the amounts of inputs. In the realm of real-time operating systems, 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 thru 2.6.22 (2003-2007), at which point it was superseded by the Completely Fair Scheduler. Overview The Linux scheduler was overhauled completely with the release of kernel 2.6 in 2003. 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Completely Fair Scheduler
The Completely Fair Scheduler (CFS) is a process scheduler that was merged into the 2.6.23 (October 2007) release of the Linux kernel and is the default scheduler of the tasks of the SCHED_NORMAL class (i.e., tasks that have no real-time execution constraints). It handles CPU resource allocation for executing processes, and aims to maximize overall CPU utilization while also maximizing interactive performance. In contrast to the previous O(1) scheduler used in older Linux 2.6 kernels, which maintained and switched run queues of active and expired tasks, the CFS scheduler implementation is based on per-CPU run queues, whose nodes are time-ordered schedulable entities that are kept sorted by red–black trees. The CFS does away with the old notion of per-priorities fixed time-slices and instead it aims at giving a fair share of CPU time to tasks (or, better, schedulable entities). Algorithm A task (i.e., a synonym for thread) is the minimal entity that Linux can schedule. However, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process (computing)
In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions concurrently. While a computer program is a passive collection of instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same program often results in more than one process being executed. Multitasking is a method to allow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Big O Notation
Big ''O'' notation is a mathematical notation that describes the limiting behavior of a function when the argument tends towards a particular value or infinity. Big O is a member of a family of notations invented by Paul Bachmann, Edmund Landau, and others, collectively called Bachmann–Landau notation or asymptotic notation. The letter O was chosen by Bachmann to stand for '' Ordnung'', meaning the order of approximation. In computer science, big O notation is used to classify algorithms according to how their run time or space requirements grow as the input size grows. In analytic number theory, big O notation is often used to express a bound on the difference between an arithmetical function and a better understood approximation; a famous example of such a difference is the remainder term in the prime number theorem. Big O notation is also used in many other fields to provide similar estimates. Big O notation characterizes functions according to their growth rate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
