This document discusses CPU scheduling in operating systems. It covers basic concepts of CPU scheduling including scheduling criteria and common algorithms like first-come first-served, shortest job first, priority scheduling, and round robin. It also discusses more advanced topics like multiple processor scheduling, real-time scheduling, and algorithm evaluation.
operating system
basic concept of c p u scheduling
scheduling critaria
scheduling algorithms
multi processor scheduling
real time scheduling
Thread scheduling
operating system Example
Java thread scheduling
Algorithms Evolution
Senthilkanth,MCA..
The following ppt's full topic covers Operating System for BSc CS, BCA, MSc CS, MCA students..
1.Introduction
2.OS Structures
3.Process
4.Threads
5.CPU Scheduling
6.Process Synchronization
7.Dead Locks
8.Memory Management
9.Virtual Memory
10.File system Interface
11.File system implementation
12.Mass Storage System
13.IO Systems
14.Protection
15.Security
16.Distributed System Structure
17.Distributed File System
18.Distributed Co Ordination
19.Real Time System
20.Multimedia Systems
21.Linux
22.Windows
cpu scheduling bassically tell us about the outer structure or the managemnet of the computer tha how it is done ,it bassically tell us about how our cpu is scheduled.
operating system
basic concept of c p u scheduling
scheduling critaria
scheduling algorithms
multi processor scheduling
real time scheduling
Thread scheduling
operating system Example
Java thread scheduling
Algorithms Evolution
Senthilkanth,MCA..
The following ppt's full topic covers Operating System for BSc CS, BCA, MSc CS, MCA students..
1.Introduction
2.OS Structures
3.Process
4.Threads
5.CPU Scheduling
6.Process Synchronization
7.Dead Locks
8.Memory Management
9.Virtual Memory
10.File system Interface
11.File system implementation
12.Mass Storage System
13.IO Systems
14.Protection
15.Security
16.Distributed System Structure
17.Distributed File System
18.Distributed Co Ordination
19.Real Time System
20.Multimedia Systems
21.Linux
22.Windows
cpu scheduling bassically tell us about the outer structure or the managemnet of the computer tha how it is done ,it bassically tell us about how our cpu is scheduled.
This Presention contains Cpu scheduling algorithms,Scheduling Criteria,process sychroization,mutilevel feed back que,critical section problem anad semaphores,Synchoroniztion hardware
This Presention contains Cpu scheduling algorithms,Scheduling Criteria,process sychroization,mutilevel feed back que,critical section problem anad semaphores,Synchoroniztion hardware
CPU Scheduling is the process through which we can find the best way to check the shortest and fastest working. Different Algorithms are explained here in this chapter. First-come-first-servers, Shortest Job First, Shortest remaining time first,
Round Robin, Priority Scheduler.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
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Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
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Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
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• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
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Ch5 cpu scheduling
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O P E R A T I N G S Y S T E M S
Module 6 : CPU Scheduling
• Basic Concepts
• Scheduling Criteria
• Scheduling Algorithms
• Multiple-Processor Scheduling
• Real-Time Scheduling
• Algorithm Evaluation
Operating System Concepts
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Chapter 6: CPU Scheduling
• Basic Concepts
• Scheduling Criteria
• Scheduling Algorithms
• Multiple-Processor Scheduling
• Real-Time Scheduling
• Algorithm Evaluation
Operating System Concepts
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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
Operating System Concepts
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Alternating Sequence of CPU And I/O Bursts
Operating System Concepts
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Histogram of CPU-burst Times
Operating System Concepts
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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.
Operating System Concepts
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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.
Operating System Concepts
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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)
Operating System Concepts
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Optimization Criteria
• Max CPU utilization
• Max throughput
• Min turnaround time
• Min waiting time
• Min response time
Operating System Concepts
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First-Come, First-Served (FCFS) Scheduling
• Example: Process Burst Time
P1 24
P2 3
P3 3
• Suppose that the processes arrive in the order: P1 , P2 , P3
The Gantt Chart for the schedule is:
• Waiting time for P1 = 0; P2 = 24; P3 = 27
• Average waiting time: (0 + 24 + 27)/3 = 17
P1 P2 P3
24 27 300
Operating System Concepts
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FCFS Scheduling (Cont.)
Suppose that the processes arrive in the order
P2 , P3 , P1 .
• The Gantt chart for the schedule is:
• Waiting time for P1 = 6; P2 = 0; P3 = 3
• Average waiting time: (6 + 0 + 3)/3 = 3
• Much better than previous case.
• Convoy effect short process behind long process
P1P3P2
63 300
Operating System Concepts
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Shortest-Job-First (SJR) Scheduling
• Associate with each process the length of its
next CPU burst. Use these lengths to schedule
the process with the shortest time.
• Two schemes:
– nonpreemptive – once CPU given to the
process it cannot be preempted until
completes its CPU burst.
– Preemptive – if a new process arrives with
CPU burst length less than remaining time of
current executing process, preempt. This
scheme is know as the
Shortest-Remaining-Time-First (SRTF).
• SJF is optimal – gives minimum average waiting
Operating System Concepts
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Process Arrival Time Burst Time
P1 0.0 7
P2 2.0 4
P3 4.0 1
P4 5.0 4
• SJF (non-preemptive)
• Average waiting time = (0 + 6 + 3 + 7)/4 - 4
Example of Non-Preemptive SJF
P1 P3 P2
73 160
P4
8 12
Operating System Concepts
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Example of Preemptive SJF
Process Arrival Time Burst Time
P1 0.0 7
P2 2.0 4
P3 4.0 1
P4 5.0 4
• SJF (preemptive)
• Average waiting time = (9 + 1 + 0 +2)/4 - 3
P1 P3P2
42 110
P4
5 7
P2 P1
16
Operating System Concepts
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Determining Length of Next CPU Burst
• Can only estimate the length.
• Can be done by using the length of previous CPU bursts, using
exponential averaging.
1. tn=actual lenght of nth
CPU burst
2. τn+1= predicted value for the next CPU burst
3 . α , 0≤α≤1
4. Define:
τn=1=α tn+(1−α)τ n .
Operating System Concepts
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Examples of Exponential Averaging
=0
n+1 = n
– Recent history does not count.
=1
– n+1 = tn
– Only the actual last CPU burst counts.
• If we expand the formula, we get:
n+1 = tn+(1 - ) tn -1 + …
+(1 - )j tn -1 + …
+(1 - )n=1 tn 0
• Since both and (1 - ) are less than or equal to 1, each
successive term has less weight than its predecessor.
Operating System Concepts
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Priority Scheduling
• A priority number (integer) is associated with each process
• The CPU is allocated to the process with the highest priority
(smallest integer highest priority).
– Preemptive
– nonpreemptive
• SJF is a priority scheduling where priority is the predicted next CPU
burst time.
• Problem Starvation – low priority processes may never execute.
• Solution Aging – as time progresses increase the priority of the
process.
Operating System Concepts
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Round Robin (RR)
• Each process gets a small unit of CPU time (time
quantum), usually 10-100 milliseconds. After this time
has elapsed, the process is preempted and added to the
end of the ready queue.
• If there are n processes in the ready queue and the time
quantum is q, then each process gets 1/n of the CPU
time in chunks of at most q time units at once. No
process waits more than (n-1)q time units.
• Performance
– q large FIFO
– q small q must be large with respect to context
switch, otherwise overhead is too high.
Operating System Concepts
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Example: RR with Time Quantum = 20
Process Burst Time
P1 53
P2 17
P3 68
P4 24
• The Gantt chart is:
• Typically, higher average turnaround than SJF, but better
response.
P1 P2 P3 P4 P1 P3 P4 P1 P3 P3
0 20 37 57 77 97 117 121 134 154 162
Operating System Concepts
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How a Smaller Time Quantum Increases Context Switches
Operating System Concepts
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Turnaround Time Varies With The Time Quantum
Operating System Concepts
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Multilevel Queue
• Ready queue is partitioned into separate
queues:
foreground (interactive)
background (batch)
• Each queue has its own scheduling algorithm,
foreground – RR
background – FCFS
• Scheduling must be done between the queues.
– Fixed priority scheduling; i.e., serve all from
foreground then from background.
Possibility of starvation.
– Time slice – each queue gets a certain
amount of CPU time which it can schedule
Operating System Concepts
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Multilevel Queue Scheduling
Operating System Concepts
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Multilevel Feedback Queue
• A process can move between the various queues; aging
can be implemented this way.
• Multilevel-feedback-queue scheduler defined by the
following parameters:
– number of queues
– scheduling algorithms for each queue
– method used to determine when to upgrade a process
– method used to determine when to demote a process
– method used to determine which queue a process will
enter when that process needs service
Operating System Concepts
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Multilevel Feedback Queues
Operating System Concepts
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Example of Multilevel Feedback Queue
• Three queues:
– Q0 – time quantum 8 milliseconds
– Q1 – time quantum 16 milliseconds
– Q2 – FCFS
• Scheduling
– A new job enters queue Q0 which is served FCFS.
When it gains CPU, job receives 8 milliseconds. If it
does not finish in 8 milliseconds, job is moved to
queue Q1.
– At Q1 job is again served FCFS and receives 16
additional milliseconds. If it still does not complete, it
is preempted and moved to queue Q2.
Operating System Concepts
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Multiple-Processor Scheduling
• CPU scheduling more complex when multiple CPUs are
available.
• Homogeneous processors within a multiprocessor.
• Load sharing
• Asymmetric multiprocessing – only one processor
accesses the system data structures, alleviating the need
for data sharing.
Operating System Concepts
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Real-Time Scheduling
• Hard real-time systems – required to complete a critical
task within a guaranteed amount of time.
• Soft real-time computing – requires that critical processes
receive priority over less fortunate ones.
Operating System Concepts
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Dispatch Latency
Operating System Concepts
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Algorithm Evaluation
• Deterministic modeling – takes a particular predetermined
workload and defines the performance of each algorithm for that
workload.
• Queuing models
• Implementation
Operating System Concepts
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Evaluation of CPU Schedulers by Simulation
Operating System Concepts