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Multilevel Queue
Multi-level queueing, used at least since the late 1950s/early 1960s, is a queue with a predefined number of levels. Items get assigned to a particular level at insert (using some predefined algorithm), and thus cannot be moved to another level (unlike in the multilevel feedback queue). Items get removed from the queue by removing all items from a level, and then moving to the next. If an item is added to a level above, the "fetching" restarts from there. Each level of the queue is free to use its own scheduling, thus adding greater flexibility than merely having multiple levels in a queue. Process Scheduling Multi-level queue scheduling algorithm is used in scenarios where the processes can be classified into groups based on property like process type, CPU time, IO access, memory size, etc. One general classification of the processes is foreground processes and background processes. In a multi-level queue scheduling algorithm, there will be 'n' number of queues, where 'n' is th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multilevel Feedback Queue
In computer science, a multilevel feedback queue is a scheduling algorithm. ''Scheduling algorithms'' are designed to have some process running at all times to keep the central processing unit (CPU) busy. The ''multilevel feedback queue'' extends standard algorithms with the following design requirements: #Separate processes into multiple ''ready queues'' based on their need for the processor. #Give preference to processes with short CPU bursts. #Give preference to processes with high I/O bursts. (I/O bound processes will sleep in the ''wait queue'' to give other processes CPU time.) The ''multilevel feedback queue'' was first developed by Fernando J. Corbató (1962). For this accomplishment, the Association for Computing Machinery awarded Corbató the Turing Award. Process scheduling Whereas the multilevel queue algorithm keeps processes permanently assigned to their initial queue assignments, the ''multilevel feedback queue'' shifts processes between queues. The shift is depen ... [...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 '' latency ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Round-robin Scheduling
Round-robin (RR) is one of the algorithms employed by process and network schedulers in computing. Guowang Miao, Jens Zander, Ki Won Sung, and Ben Slimane, Fundamentals of Mobile Data Networks, Cambridge University Press, , 2016. As the term is generally used, time slices (also known as time quanta) are assigned to each process in equal portions and in circular order, handling all processes without priority (also known as cyclic executive). Round-robin scheduling is simple, easy to implement, and starvation-free. Round-robin scheduling can be applied to other scheduling problems, such as data packet scheduling in computer networks. It is an operating system concept. The name of the algorithm comes from the round-robin principle known from other fields, where each person takes an equal share of something in turn. Process scheduling To schedule processes fairly, a round-robin scheduler generally employs time-sharing, giving each job a time slot or ''quantum'' (its allow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FIFO (computing And Electronics)
Representation of a FIFO queue In computing and in systems theory, FIFO is an acronym for first in, first out (the first in is the first out), a method for organizing the manipulation of a data structure (often, specifically a data buffer) where the oldest (first) entry, or "head" of the queue, is processed first. Such processing is analogous to servicing people in a queue area on a first-come, first-served (FCFS) basis, i.e. in the same sequence in which they arrive at the queue's tail. FCFS is also the jargon term for the FIFO operating system scheduling algorithm, which gives every process central processing unit (CPU) time in the order in which it is demanded. FIFO's opposite is LIFO, last-in-first-out, where the youngest entry or "top of the stack" is processed first. A priority queue is neither FIFO or LIFO but may adopt similar behaviour temporarily or by default. Queueing theory encompasses these methods for processing data structures, as well as interactions b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multilevel
Multilevel or multi-level may refer to: * A hierarchy, a system where items are arranged in an "above-below" relation. * A system that is composed of several layers. * Bombardier MultiLevel Coach The Bombardier MultiLevel Coach is a bi-level passenger rail car manufactured by Bombardier for use on commuter rail lines. The first units were delivered in 2006 and deliveries (in various orders) continued to 2014. Overview There are 643 o ..., a passenger rail car by Bombardier. See also * * {{dab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fair-share Scheduling
Fair-share scheduling is a scheduling algorithm for computer operating systems in which the CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ... usage is equally distributed among system users or groups, as opposed to equal distribution of resources among processes. One common method of logically implementing the fair-share scheduling strategy is to recursively apply the round-robin scheduling strategy at each level of abstraction (processes, users, groups, etc.) The time quantum required by round-robin is arbitrary, as any equal division of time will produce the same results. This was first developed by Judy Kay and Piers Lauder through their research at Sydney University in the 1980s. For example, if four users (A,B,C,D) are concurrently executing one process each, the sche ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lottery Scheduling
Lottery scheduling is a probabilistic scheduling algorithm for processes in an operating system. Processes are each assigned some number of lottery tickets, and the scheduler draws a random ticket to select the next process. The distribution of tickets need not be uniform; granting a process more tickets provides it a relative higher chance of selection. This technique can be used to approximate other scheduling algorithms, such as Shortest job next and Fair-share scheduling. Lottery scheduling solves the problem of starvation Starvation is a severe deficiency in caloric energy intake, below the level needed to maintain an organism's life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, dea .... Giving each process at least one lottery ticket guarantees that it has non-zero probability of being selected at each scheduling operation. Implementation Implementations of lottery scheduling should tak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
