7 - CPU Scheduling Basic Concepts Scheduling Criteria...

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CPU Scheduling Basic Concepts Scheduling Criteria Scheduling Algorithms
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Basic Concepts Maximum CPU utilization obtained with multiprogramming CPU–I/O Burst Cycle – Process execution consists of a cycle of CPU execution and I/ O wait CPU burst distribution
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Alternating Sequence of CPU And I/ O Bursts
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Histogram of CPU-burst Times
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CPU Scheduler Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them CPU scheduling decisions may take place when a process: 1. Switches from running to waiting state 2. Switches from running to ready state 3. Switches from waiting to ready 4. Terminates Scheduling under 1 and 4 is nonpreemptive All other scheduling is preemptive
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Dispatcher Dispatcher module gives control of the CPU to the process selected by the short-term scheduler; this involves: switching context switching to user mode jumping to the proper location in the user program to restart that program Dispatch latency – time it takes for the dispatcher to stop one process and start another running
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Scheduling Criteria CPU utilization – keep the CPU as busy as possible Throughput – # of processes that complete their execution per time unit Turnaround time – amount of time to execute a particular process Waiting time – amount of time a process has been waiting in the ready queue Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment)
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Optimization Criteria Max CPU utilization Max throughput Min turnaround time Min waiting time Min response time
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