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process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. ? Preemptive: allows a process to be interrupted. ? Non- Preemptive: allows a process finishes with its current CPU burst. ? Scheduling under 1 and 4 is nonpreemptive. ? All other
24 Feb 2012 Process Scheduling. Deciding which process/thread should occupy each resource. (CPU, disk, etc.) at each moment. Scheduling is everywhere • disk reads. • process/thread resource allocation. • servicing clients in a web server. • compute jobs in clusters / data centers. • jobs using physical machines in
Priorities can be set internally (by scheduler) or externally (by users). • Dynamic vs Static. – Static priority : priority of a process is fixed. – Dynamic priority : scheduler can change the process priority during execution in order to achieve scheduling goals. • eg1. decrease priority of a process to give another process a.
Scheduling Algorithm Goals. • Be fair (to processes? To users?) • Be efficient: Keep CPU busy and don't spend a lot of time deciding! • Maximize throughput: minimize time users must wait. • Minimize response time. • Be predictable: jobs should take about the same time to run when run multiple times. • Minimize overhead.
Different from Multilevel Queue. Scheduling by Allowing Processes to. Migrate Among Queues. ? Configurable Parameters: a. # of queues b. The scheduling algorithm for each queue c. The method to determine when to upgrade a process to a higher priority queue. d. The method to determine when to demote a process to a
5: CPU-Scheduling. 2. What Is In This Chapter? • This chapter is about how to get a process attached to a processor. • It centers around efficient algorithms that perform well. • The design of a scheduler is concerned with making sure all users get their fair share of the resources. CPU Scheduling
q Long-term scheduler (or job scheduler). Q Which processes should be brought into the ready queue. Q Invoked very infrequently (seconds, minutes) ?. (may be slow). Q Controls the degree of multiprogramming q Short-term scheduler (or CPU scheduler). Q Which process should execute next (allocates. CPU). Q Invoked
5.2. Chapter 5: Process Scheduling. 5.1. Basic Concepts. 5.2. Scheduling Criteria. 5.3. Scheduling Algorithms. 5.3.1. First-Come, First-Served Scheduling. 5.3.2. Shortest-Job-First Scheduling. 5.3.3. Priority Scheduling. 5.3.4. Round-Robin Scheduling. 5.3.5. Multilevel Queue Scheduling. 5.4. Multiple-Processor Scheduling.
ECS 150 (Operating Systems). Process Scheduling. 1. Process Scheduling. Process Scheduling. Goal. What characterizes a “fair internal policy?" Which process is given the CPU next? This is the province of schedulers.
Recall. Basics. Algorithms. Multi-Processor Scheduling. PCB process state process ID (number). PC. Registers memory information open files other resources. Job Queue. Linked list of PCBs. (main) job queue ready queue device queues. Schedulers. Long-term/Job scheduler. (loads from disk). Short-term/CPU scheduler.
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