OS Mini Project

7/28/2019 OS Mini Project

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BITI / S1G1

OPERATING SYSTEMS

(BITS 1213)

GROUP MEMBERS

SOO PHENG KIAN B031210015

ANDY LOW FOO HWA B031210343

MOHAMAD ALIFF AIMAN BIN YUSOF B031210368

NUR AFIQAH BINTI ABDUL RAHMAN B031210210

LECTURER`S NAME : DR. NURUL AZMA ZAKARIA


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Type of Processor Scheduling

Long-term: which process to be admitted

Medium-term: which process to swap in or out

Short-term: which ready process to execute next


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Priorities

Scheduler will always choose a process with highpriority 1st over the low priority process

Have multiple queues to represent each level ofpriority

Lower priority may suffer starvation- allow a low priority process to change its priority based on its ages and

execute history

Decision mode Non-preemptive: When a process is in running state, it will continue

until it is terminated or block itself for I/O

Preemptive: -currently running process will be interrupted and move toready state by OS

-Allow for better service to avoid 1 process monopolize theprocessor very long


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Shortest-Job-First Scheduling(SJF)

To pick a quickest fastest little job that need to

be done and get it out 1st, and pick the next

smallest faster job to do next.

The SJF algorithm can be preemptive or non-

preemptive.

Preemptive: will preempt the currently executing process

Non-preemptive: allow the currently running process tofinish its CPU burst.


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Shortest Remaning Time

Process with the shortest expected CPU burst time will

be process 1st.

A process may preempt when another process becomeready.

The decision mode is preemptive.

I/O bound process will be picked 1st.


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MULTIPROCESSOR SCHEDULING

Can be classify multiprocessor system as :

Loosely coupled / distributed multiprocessor / cluster

each processor having its own memory and I/O channel.Functionally specialized processors

controlled by the master and provide services to it.

Tightly coupled multiprocessor

set of processors that shared main memory and under control of operating system.

oGranularity

Grain Size Description Synchronization

Interval

Fine Parallelism inherent in a single instruction stream


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Assignment of processes to

processors

the question arise about to

whether the assignment should bestatic or dynamic.

The use of multiprogramming onindividual processors

for individuals processor should beable to switch among a number of

processes to achieve high utilization

and therefore better performance but

not for medium-grained application.

Process dispatching the use of priorities or of

sophisticated scheduling algorithms

based on past usage may improve

performance over a simple-minded

first-come-first-served strategy.

o Design Issues


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Gang Scheduling

A set of related threads is scheduled to run on a set of processors at the same time, on a

one-to-one basis

Dedicated processor assignment

This is the opposite of the load-sharing approach and provides implicit scheduling

defined by the assignment of threads to processors. Each program, for the duration of its

execution, is allocated a number of processors equal to the number of threads in the

program. When the program terminates, the processors return to the general pool for

possible allocation to another program.

Dynamic Scheduling

the number of threads in a process can be altered during the course of execution.


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Real Time Computing

Correctness of system depends to the logical result and the timewhich the results are produced.

Hard Real-Time Task

We must meet its deadline,otherwise fatal damage r error will occur

Soft Real-Time Task

We should meet is deadline but not mandatory and schedule it evenif the deadline is already passed.

Aperiodic Test

Random task which may have a constraint on start or finish time or

both.

Periodic Task

A sequence of tasks which appear once per period T.


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Determnistic

# Operations are performed at fixed,predetermined times or within

predetermined time intervals

# Concern how long the OS delays before acknowledging an interrupt

# Maximal delay is small

Responsiveness

# How long,after acknowledgment,it takes the OS to service the

interrupt.

# This includes

-Amount of time to begin execution of the interrupt

-Amount of time to perform the interrupt


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User Control

# Its includes user specifies priority,specify paging,whatprocesses must always reside in main memory,disks

algorithms to use and rights of processes.

Reliability

# More important for real-time system than regular system

# Error generally not recoverable# Attempt either to correct the problem or minimize is effects

while continuing to run and most critical,high priority tasksexecute.


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Fast process/thread switch

Small size

Ability to respond to external interrupts

quickly Preemptive scheduling base on priority

Delay tasks for fixed amount of time

Special alarms and timeouts


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Operating system is responsible for using disk drive efficiently,having afast access time and disk bandwidth.

Access time has 2 major components.->time for the disk to move the heads to the cylinder

containing desired sector.-> additional time waiting for the disk to rotate the

desired sector to the disk head.

Disk Bandwidth is the total number of bytes transferred, dividedby the total time between the first request for service and thecompletion of the last transfer.

To minimize seek time.

Seek time Seek distance

For example, we take a request queue (0-199).

98, 183, 37, 122, 14, 124, 65, 67

Initial value=53


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First Come First Serve(FCFS)

Request runsequentially.

All processes are fair.

Random scheduling ifthere are many

processes.Also can be known asFirst In First Out(FIFO).


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Shortest Seek Time First(SSTF)

Selects the requestwith the minimumseek time from thecurrent headposition.

May cause starvationof some requests.

Job on the far endwill starve whereasclosest job will keepgetting serviced.


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Elevator Algorithm or SCAN

The disk arm starts atone end of the disk, andmoves toward the otherend, servicing requestsuntil it gets to the otherend of the disk, where

the head movement isreversed and servicingcontinues.

Avoids starvation.

Provides good

performance.Fair to all request/job.


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C-SCAN

Provides a moreuniform wait timethan SCAN.

The head movesfrom one end of thedisk to the other.servicing requests asit goes. When itreaches the otherend, however, itimmediately returns

to the beginning ofthe disk, withoutservicing anyrequests on thereturn trip.


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C-LOOK

Version of C-SCAN Arm only goes as far

as the last request ineach direction, thenreverses directionimmediately,without first going allthe way to the end ofthe disk.


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Comparison and Conclusion

Performance depends on the number and types ofrequests.

Requests for disk service can be influenced by the file-allocation method.

The disk-scheduling algorithm should be written as aseparate module of the operating system, allowing it tobe replaced with a different algorithm if necessary.

SSTF is common and has a natural appeal

SCAN and C-SCAN perform better for systems thatplace a heavy load on the disk.

SSTF or LOOK is a reasonable choice for the defaultalgorithm.

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