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Module 19: Multi-core computing Operating Systems
Lecture 37: Multi-core computing CPU Scheduling
The Lecture Contains:
Contents
Scheduling
CPU Scheduling
When to Have CPU Scheduling
Scheduling Criteria
Scheduling Algorithms
Example (Contd.)
SJF
Example of “Guessing”
Preemptive SJF
Example (SRTF)
Adding Priority (Priority Scheduling)
Priority Scheduling + SJF
Module 19: Multi-core computing Operating Systems
Lecture 37: Multi-core computing CPU Scheduling
Multi-core computing
Operating Systems
Contents
Scheduling Traditional Real time Multi-processor Synchronization and synchronization objects Inter-process communication Security
Multi-core computing
CPU Scheduling
Scheduling
To hide the effects of I/O Bursts and achieve higher CPU utilization To give a fair chance to all processes Short term scheduling CPU scheduling Long term scheduling Process admission policies Medium term scheduling Swap management
Module 19: Multi-core computing Operating Systems
Lecture 37: Multi-core computing CPU Scheduling
Scheduling Criteria
CPU Utilization (System centric) Keep CPU as much busy as possible Throughput (System centric) Number of processes completed/time Turnaround time (Process centric) Real time taken to complete a process Waiting time (Process centric) How much time a process is in ready queue Response time (Process centric) Factor for an interactive process Deadline (Real time behavior) Time guarantee to schedule a task.
Scheduling Algorithms
First Come First Serve (FCFS) Simplest implementation No preemption Shortest Job First (SJF) Optimal scheduling algorithm Minimum Average Waiting Time Difficulty: To know the time that it will take Batch systems: A good choice.
Module 19: Multi-core computing Operating Systems
Lecture 37: Multi-core computing CPU Scheduling
Example
Process Arrival Time CPU Burst Wait Time Turnaround P1 0 6 0 6 P2 4 20 2 22 P3 5 1 21 22
Example (Contd.)
Process Arrival Time CPU Burst Wait Time Turnaround P1 0 6 0 6 P2 4 20 3 23 P3 5 1 1 2
Module 19: Multi-core computing Operating Systems
Lecture 37: Multi-core computing CPU Scheduling
Preemptive SJF
When a new task arrives, the SJF is evaluated again and rescheduling can take place. aka Shortest-remaining-time-first (SRTF) scheduling
Example (SRTF)
Adding Priority (Priority Scheduling)
Simplest form is to add priority to a process. Select the highest priority job first Apply SJF/SRTF/FIFO/… scheduling only within a group of processes with the same priority
Priority scheduling + SJF
