Preemptive vs Nonpreemptive Scheduling

ShorttermischediaPreemptive Scheduling

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In preemptive scheduling each process gets a slice

of cpu.sk metorun.to

The running process canbe fiercely removedfrom

the CPU underfollowing conditions

Timeslice expires n dy

running ready2 An interrupt occurs on the CPU

A higher priority processenters the ready queue

NEW READY

WAITING READYt

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Nonpreemptifescheduling

In nonpreemptive scheduling therunning process

cannot be forcefully removed from the CPU

A running process holds the Cputill

gt terminates

2 St switches from tat

on its own because of

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emptive Microsoftwindows3IOt All windowsversion afterwindows

Mac OS Linux1 1 1

Cost of Preemptive scheduling

1 sharing data between processes

when one process is p edata itgets

preemptedr

Gf some otherness triestoreadthis data

it will find this datain inconsistent data

Different mechanisms like spinifex weredeveloped to nataees

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Forehead of guarding shared dataininterrupts

whenever an interrupt happens an interrupt

handleriscalled

What if the same interrupt happenson two

CPU's and the interrupt handler sharesdata

Need to use ex to protect criticalsection

3 Increases the complexidsgnwhat happens when the Kernel is changing

some important data I o queuesand gets

preempted in middle D DD

what if the kernel againtries to modify this

data on behalf of some different process

system d

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