5 CPU Scheduling (1) - PowerPoint PPT Presentation

. . March 26, 2014 March 26, 2014 . . . . . . . . . . . 1 / 61 操作系统原理与设计 第 5 章 CPU Scheduling (1) 陈香兰 中国科学技术大学计算机学院 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 for a particular system. To discuss evaluation crieria for selecting a CPU-scheduling algorithm To describe various CPU-scheduling algorithms. To introduce CPU scheduling. . . . . . . . . Chapter Objectives . . . . . 2 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. 6 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . .. OS examples . . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 4 .. . .. . . . . . . Scheduling Algorithms . 1 Basic Concepts . .. 2 Scheduling Criteria . .. 3 3 / 61 提纲—— CPU scheduling (1) 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 Maximum CPU utilization . . . . . . . . Objective of multiprogramming . CPU scheduling is the basis of multiprogrammed OSes . Almost all computer resources are scheduled before use. Scheduling is a fundamental OS function . . . . . Basic Concepts . . . . . . . 4 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. .. .. 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . 6 . OS examples . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . Scheduling Algorithms 3 1 . . . . Outline . . . .. .. Basic Concepts CPU-I/O Burst Cycle CPU Scheduler Preemptive Scheduling Dispatcher . .. 2 Scheduling Criteria . 5 / 61 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 + CPU execution = n (CPU execution + I/O wait) Process execution Begin and end with a CPU burst I/O Bursts Alternating Sequence of CPU And of CPU execution and I/O wait Process execution consists of a cycle CPU-I/O Burst Cycle A property of process : Basic Concepts: CPU-I/O Burst Cycle . . . . 6 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . . . . . CPU burst distribution Histogram of CPU-burst Times March 26, 2014 7 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. .. .. 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . 6 . OS examples . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . Scheduling Algorithms 3 1 . . . . Outline . . . .. .. Basic Concepts CPU-I/O Burst Cycle CPU Scheduler Preemptive Scheduling Dispatcher . .. 2 Scheduling Criteria . 8 / 61 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 an unordered linked list? a tree? a priority queue? a FIFO Queue? Ready Queue could be: execute and allocates the CPU to the process selects a process from the processes in memory that are ready to CPU scheduler (Short-term Scheduler) CPU Scheduler . . . . 9 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. .. .. 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . 6 . OS examples . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . Scheduling Algorithms 3 1 . . . . Outline . . . .. .. Basic Concepts CPU-I/O Burst Cycle CPU Scheduler Preemptive Scheduling Dispatcher . .. 2 Scheduling Criteria . 10 / 61 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 For 2 & 3, schedule? VS. not schedule? For 1 & 4, must schedule; Terminates 4 . . . Switches from waiting to ready 3 . . . Switches from running to ready state 2 . . . . . Preemptive Scheduling I CPU scheduling decisions may take place when a process: . . . 1 Switches from running to waiting state . . 11 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 If one process is preempted while it is updating the data. . . . . . . . . Two processes sharing data . usually needs a hardware timer, synchronization overhead Mac OS X . . . . Preemptive Scheduling II The scheduling scheme: Windows 3.x before Mac OS X Windows 95 & ... 12 / 61 nonpreemptive( 非抢占式 ) : only 1 & 4 otherwise preemptive( 抢占式 ) data is in an inconsistent( 不一致 ) state 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 synchronization overhead with shared data. needs special HW, for example, a timer. . . . . . . . . COST for preemption . Preemptive Scheduling III . . . . 13 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 some synchronization mechnisms disable interrupt new mechnisms are needed, such as Interrupt affected code VS normal kernel code ? preemptive kernel VS. nonpreemptive kernel ? . . . . . . . some activities that changes important kernel data? What happens if the process is preempted in the middle of Preemption of the OS kernel . . . . 14 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. .. .. 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . 6 . OS examples . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . Scheduling Algorithms 3 1 . . . . Outline . . . .. .. Basic Concepts CPU-I/O Burst Cycle CPU Scheduler Preemptive Scheduling Dispatcher . .. 2 Scheduling Criteria . 15 / 61 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. switching context March 26, 2014 SHOULD be as fast as possible process and start another running program jumping to the proper location in the user program to restart that . switching to user mode selected by the short-term scheduler ; this involves: Dispatcher module gives control of the CPU to the process Dispatcher . . . . 16 / 61 Dispatch latency – time it takes for the dispatcher to stop one 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. interrupt March 26, 2014 execution process real-time dispatch latency available process made . processing 17 / 61 . response interval response to event event . Dispatch latency . . ✛ ✲ ✛ ✲ ✛ ✲ ✛ ✲ ✛ conflicts ✲✛ dispatch ✲ 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. 6 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . .. OS examples . . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . .. Scheduling Algorithms .. . . . . Outline . . 3 . 1 Basic Concepts . .. 2 Scheduling Criteria Scheduling Criteria . .. 18 / 61 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . . . . . Scheduling Criteria I possible March 26, 2014 19 / 61 CPU utilization （ CPU 利用率）– keep the CPU as busy as conceptually: 0 % ∼ 100 % ; in a real system: 40 % ∼ 90 % 4 核 8 线程编译 Linux 内核时的 CPU 利用率情况（ 0 ˜ 7, 总） 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. for short transactions : may be 10 processes per second March 26, 2014 for time-sharing environment submit ted until the first response is produced, not output ready queue ready queue , executing on the CPU, and doing I/O . = the periods spent waiting to get into memory , waiting in the from the time of submission of a process to the time of completion . particular process for long processes : may be 1 process per hour different from one process set to another process set execution per time unit Scheduling Criteria II . . . . 20 / 61 Throughput （吞吐率）– # of processes that complete their Turnaround time ( 周转时间 ) – amount of time to execute a Waiting time – amount of time a process has been waiting in the Response time – amount of time it takes from when a request was 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. . March 26, 2014 different from system to system. . . . . . . . Stability? Average? response time waiting time turnaround time Minimize? throughput CPU utilization Maximize? Optimization Criteria . . . . 21 / 61 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计

. .. .. 4 Multiple-Processor Scheduling . .. 5 Real-Time Scheduling . 6 . OS examples . .. 7 Algorithm Evaluation . .. 8 March 26, 2014 . 22 / 61 Priority Scheduling Basic Concepts . . . . Outline . . . .. 1 . .. 2 Scheduling Criteria . .. 3 Scheduling Algorithms FCFS Scheduling SJF Scheduling Round Robin( 时间片轮转 ) Scheduling Multilevel Queue （多级队列） Scheduling Multilevel Feedback Queue （多级反馈队列） Scheduling 小结和作业 陈香兰 ( 中国科学技术大学计算机学院 ) 操作系统原理与设计