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Shortest Job First
Shortest job next (SJN), also known as shortest job first (SJF) or shortest process next (SPN), is a scheduling policy that selects for execution the waiting process with the smallest execution time. SJN is a non- preemptive algorithm. Shortest remaining time is a preemptive variant of SJN. Shortest job next is advantageous because of its simplicity and because it minimizes the average amount of time each process has to wait until its execution is complete. However, it has the potential for process starvation for processes which will require a long time to complete if short processes are continually added. Highest response ratio next is similar but provides a solution to this problem using a technique called aging. Another disadvantage of using shortest job next is that the total execution time of a job must be known before execution. While it is impossible to predict execution time perfectly, several methods can be used to estimate it, such as a weighted average of previous e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shortest Job First
Shortest job next (SJN), also known as shortest job first (SJF) or shortest process next (SPN), is a scheduling policy that selects for execution the waiting process with the smallest execution time. SJN is a non- preemptive algorithm. Shortest remaining time is a preemptive variant of SJN. Shortest job next is advantageous because of its simplicity and because it minimizes the average amount of time each process has to wait until its execution is complete. However, it has the potential for process starvation for processes which will require a long time to complete if short processes are continually added. Highest response ratio next is similar but provides a solution to this problem using a technique called aging. Another disadvantage of using shortest job next is that the total execution time of a job must be known before execution. While it is impossible to predict execution time perfectly, several methods can be used to estimate it, such as a weighted average of previous e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheduling Algorithm
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] |
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] |
Preemption (computing)
In computing, preemption is the act of temporarily interrupting an executing task, with the intention of resuming it at a later time. This interrupt is done by an external scheduler with no assistance or cooperation from the task. This preemptive scheduler usually runs in the most privileged protection ring, meaning that interruption and resuming are considered highly secure actions. Such a change in the currently executing task of a processor is known as context switching. User mode and kernel mode In any given system design, some operations performed by the system may not be preemptable. This usually applies to kernel functions and service interrupts which, if not permitted to run to completion, would tend to produce race conditions resulting in deadlock. Barring the scheduler from preempting tasks while they are processing kernel functions simplifies the kernel design at the expense of system responsiveness. The distinction between user mode and kernel mode, whi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shortest Remaining Time
Shortest remaining time, also known as shortest remaining time first (SRTF), is a scheduling method that is a preemptive version of shortest job next scheduling. In this scheduling algorithm, the process with the smallest amount of time remaining until completion is selected to execute. Since the currently executing process is the one with the shortest amount of time remaining by definition, and since that time should only reduce as execution progresses, the process will either run until it completes or get preempted if a new process is added that requires a smaller amount of time. Shortest remaining time is advantageous because short processes are handled very quickly. The system also requires very little overhead since it only makes a decision when a process completes or a new process is added, and when a new process is added the algorithm only needs to compare the currently executing process with the new process, ignoring all other processes currently waiting to execute. Lik ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process Starvation
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific service or product for customers *Business process modeling, activity of representing processes of an enterprise in order to deliver improvements *Manufacturing process management, a collection of technologies and methods used to define how products are to be manufactured. *Process architecture, structural design of processes, applies to fields such as computers, business processes, logistics, project management *Process costing, a cost allocation procedure of managerial accounting * Process management, ensemble of activities of planning and monitoring the performance of a business process or manufacturing processes *Process management (project management), a systematic series of activities directed towards causing an end result in engineeri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Highest Response Ratio Next
Highest response ratio next (HRRN) scheduling is a non-preemptive discipline. It was developed by Brinch Hansen as modification of shortest job next or shortest job first (SJN or SJF) to mitigate the problem of process starvation. In HRRN, the next job is not that with the shortest estimated run time, but that with the highest response ratio defined as response\ ratio = \frac = 1 + \frac This means, the jobs that have spent a long time waiting compete against those estimated to have short run times. As you can see in the above equation of response ratio, if the waiting time of a process increases, its response ratio increases making the long-awaited process to execute next. So, this algorithm solves the starvation problem that exists in SJN scheduling algorithm. Algorithm Given a Linked list Q, iterate through Q to find the highest ratio by comparing each ratio within the queue. Once a ratio of element N is greater than the element M with the highest ratio replace element M wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aging (scheduling)
In computer science for Operating systems, aging (US English) or ageing is a scheduling technique used to avoid starvation. Fixed priority scheduling is a scheduling discipline, in which tasks queued for utilizing a system resource are assigned a priority each. A task with a high priority is allowed to access a specific system resource before a task with a lower priority is allowed to do the same. A disadvantage of this approach is that tasks assigned with a lower priority may be starved when a large number of high priority tasks are queued. Aging is used to gradually increase the priority of a task, based on its waiting time in the ready queue. Problem In priority-based scheduling algorithms 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 ca ..., a major problem is indefinite block ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multilevel Feedback Queue
In computer science, a multilevel feedback queue is a scheduling (computing), 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 bound, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agile Development
In software development, agile (sometimes written Agile) practices include requirements discovery and solutions improvement through the collaborative effort of self-organizing and cross-functional teams with their customer(s)/ end user(s), adaptive planning, evolutionary development, early delivery, continual improvement, and flexible responses to changes in requirements, capacity, and understanding of the problems to be solved. Popularized in the 2001 ''Manifesto for Agile Software Development'', these values and principles were derived from and underpin a broad range of software development frameworks, including Scrum and Kanban. While there is much anecdotal evidence that adopting agile practices and values improves the effectiveness of software professionals, teams and organizations, the empirical evidence is mixed and hard to find. History Iterative and incremental software development methods can be traced back as early as 1957, Gerald M. Weinberg, as quoted in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cost Of Delay
Cost of Delay is "a way of communicating the impact of time on the outcomes we hope to achieve". More formally, it is the partial derivative of the ''total expected value'' with respect to ''time''. Cost of Delay combines an understanding of value with how that value leaks away over time. It is a tactic that helps communicate and prioritize development decisions by calculating the impact of time on value creation & capture. More simply, it is the answer to the question: "What would it cost us if this was delayed by 1 month?". Or, alternatively, "what would it be worth to us if we could get this 1 month earlier?" Cost of Delay has the units of $/time. The Delay Cost incurred (as a result of a delay) is found by integrating Cost of Delay over a specific time period. Cost of Delay in Product Development Cost of Delay is described by Don Reinertsen as being the "one thing" to quantify. "We need Cost of Delay to evaluate the cost of queues, the value of excess capacity, the benefit of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
