|
Weighted Round Robin
Weighted round robin (WRR) is a network scheduler for data flows, but also used to schedule processes. Weighted round robin is a generalisation of round-robin scheduling. It serves a set of queues or tasks. Whereas round-robin cycles over the queues or tasks and gives one service opportunity per cycle, weighted round robin offers to each a fixed number of opportunities, as specified by the configured weight which serves to influence the portion of capacity received by each queue or task. In computer networks, a service opportunity is the emission of one packet, if the selected queue is non-empty. If all packets have the same size, WRR is the simplest approximation of generalized processor sharing (GPS). Several variations of WRR exist. The main ones are the ''classical'' WRR, and the ''interleaved'' WRR. Algorithm Principles WRR is presented in the following as a network scheduler. It can also be used to schedule tasks in a similar way. A weighted round-robin network sch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Scheduler
A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an arbiter on a node in a packet switching communication network. It manages the sequence of network packets in the transmit and receive queues of the protocol stack and network interface controller. There are several network schedulers available for the different operating systems, that implement many of the existing network scheduling algorithms. The network scheduler logic decides which network packet to forward next. The network scheduler is associated with a queuing system, storing the network packets temporarily until they are transmitted. Systems may have a single or multiple queues in which case each may hold the packets of one flow, classification, or priority. In some cases it may not be possible to schedule all transmissions within the constraints of the system. In these cases the network scheduler is responsible for deciding which traffic to forward and what ge ... [...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 allowance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generalized Processor Sharing
Generalized processor sharing (GPS) is an ideal scheduling algorithm for scheduling (computing), process schedulers and network schedulers. It is related to the Fair queuing#FQ Principle, fair-queuing principle which groups packets into classes and shares the service capacity between them. GPS shares this capacity ''according to some fixed weights''. In process scheduling, GPS is "an idealized scheduling algorithm that achieves perfect fairness. All practical schedulers approximate GPS and use it as a reference to measure fairness." Generalized processor sharing assumes that traffic is fluid (infinitesimal packet sizes), and can be arbitrarily split. There are several service disciplines which track the performance of GPS quite closely such as weighted fair queuing (WFQ), also known as packet-by-packet generalized processor sharing (PGPS). Justification In a network such as the internet, different application types require different levels of performance. For example, email is a ... [...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 allowance ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Work-conserving Scheduler
In computing and communication systems, a work-conserving scheduler is a scheduler that always tries to keep the scheduled resource(s) busy, if there are submitted jobs ready to be scheduled. In contrast, a non-work conserving scheduler is a scheduler that, in some cases, may leave the scheduled resource(s) Idle (CPU), idle despite the presence of jobs ready to be scheduled. For example, when dealing with Network scheduler, networking and packet scheduling, a work-conserving scheduler leaves the channel idle only when there are no packets to transmit, whereas a non-work conserving scheduler might leave the channel idle with Network packet, packets still pending Transmission (telecommunications), transmission. Similarly, when referring to Scheduling (computing), CPU scheduling, i.e. Threads (computer science), threads or processes scheduled over one or more available Computer processor, processors or Processor core, cores, a work-conserving scheduler ensures that processors/cores are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Starvation (computer Science)
In computer science, resource starvation is a problem encountered in concurrent computing where a process is perpetually denied necessary resources to process its work. Starvation may be caused by errors in a scheduling or mutual exclusion algorithm, but can also be caused by resource leaks, and can be intentionally caused via a denial-of-service attack such as a fork bomb. When starvation is impossible in a concurrent algorithm, the algorithm is called starvation-free, lockout-freed or said to have finite bypass. This property is an instance of liveness, and is one of the two requirements for any mutual exclusion algorithm; the other being correctness. The name "finite bypass" means that any process (concurrent part) of the algorithm is bypassed at most a finite number times before being allowed access to the shared resource. Scheduling Starvation is usually caused by an overly simplistic scheduling algorithm. For example, if a (poorly designed) multi-tasking system always swi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generalized Processor Sharing
Generalized processor sharing (GPS) is an ideal scheduling algorithm for scheduling (computing), process schedulers and network schedulers. It is related to the Fair queuing#FQ Principle, fair-queuing principle which groups packets into classes and shares the service capacity between them. GPS shares this capacity ''according to some fixed weights''. In process scheduling, GPS is "an idealized scheduling algorithm that achieves perfect fairness. All practical schedulers approximate GPS and use it as a reference to measure fairness." Generalized processor sharing assumes that traffic is fluid (infinitesimal packet sizes), and can be arbitrarily split. There are several service disciplines which track the performance of GPS quite closely such as weighted fair queuing (WFQ), also known as packet-by-packet generalized processor sharing (PGPS). Justification In a network such as the internet, different application types require different levels of performance. For example, email is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IP Network
The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP). In the development of this networking model, early versions of it were known as the Department of Defense (DoD) model because the research and development were funded by the United States Department of Defense through DARPA. The Internet protocol suite provides End-to-end principle, end-to-end data communication specifying how data should be packetized, addressed, transmitted, routing, routed, and received. This functionality is organized into four abstraction layers, which classify all related protocols according to each protocol's scope of networking. An implementation of the layers for a particular application forms a protoco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deficit Round Robin
Deficit Round Robin (DRR), also Deficit Weighted Round Robin (DWRR), is a scheduling algorithm for the network scheduler. DRR is, like weighted fair queuing (WFQ), a packet-based implementation of the ideal Generalized Processor Sharing (GPS) policy. It was proposed by M. Shreedhar and G. Varghese in 1995 as an efficient (with ''O(1)'' complexity) and fair algorithm. Details In DRR, a scheduler handling N flows is configured with one quantum Q_i for each flow. This global idea is that, at each round, the flow i can send at most Q_i bytes, and the remaining, if any, is reported to the next round. In this way, the flow of number will achieve a minimal long term data rate of \fracR, where R is the link rate. Algorithm The DRR scans all non-empty queues in sequence. When a non-empty queue i is selected, its deficit counter is incremented by its quantum value. Then, the value of the deficit counter is a maximal number of bytes that can be sent at this turn: if the deficit counter i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weighted Fair Queuing
Weighted fair queueing (WFQ) is a network scheduling algorithm. WFQ is both a packet-based implementation of the generalized processor sharing (GPS) policy, and a natural extension of fair queuing (FQ). Whereas FQ shares the link's capacity in equal subparts, WFQ allows schedulers to specify, for each flow, which fraction of the capacity will be given. Weighted fair queuing is also known as packet-by-packet GPS (PGPS or P-GPS) since it approximates generalized processor sharing "to within one packet transmission time, regardless of the arrival patterns." Parametrization and fairness Like other GPS-like scheduling algorithms, the choice of the weights is left to the network administrator. There is no unique definition of what is "fair" (see for further discussion). By regulating the WFQ weights dynamically, WFQ can be utilized for controlling the quality of service, for example, to achieve guaranteed data rate. Proportionally fair behavior can be achieved by setting the we ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
