-Process Management Ppt

7/25/2019 -Process Management Ppt

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Process management

Allocates resources to processes

Enables processes to share and exchange

information

Protects the resources of each process from

other processes

Provides facilities for process sharing and

synchronization

Schedules the work done by the processor


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Process

an instance of a program in execution

Program

consists of only 3 statements

can either be !" bound

#P$ bound


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%igure 3&'

Process State (ransition )iagram


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Process Scheduler

3 (ypes of schedulers

*ong+term scheduler ,-ob ! admission.

Short+term scheduler ,cpu.

/edium+term scheduler ,/idterm.


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"S Scheduler

*ong+term Scheduler

)ecides which of the new processes

are added to the pool of processes

ready for execution0

and determines which of the

processes is to be released orterminated


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/edium+term Scheduler

)ecides which of the processes

should be partially or fully loaded0

suspended or to resume in the main

memory


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Short+term Scheduler

)ecides as to which of the available

processes will be allotted the

processor and for how long


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Process Scheduling

#P$ Scheduling

se1uence or order of process

execution as they are allotted the

processor&

#P$ Scheduling Algorithm

(he many ways of allotting the

processor to a specific -ob or process


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(he main purposes of scheduling

algorithms are

to minimize resource starvation

to ensure fairness among the parties

utilizing the resources


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Evaluation #riteria of the best

#P$ scheduling algorithm

ncrease #P$ $tilization

/ake #P$ busy processing at all times

2 time the processor is busy

ncrease throughput

measures how much work is done in a given time

educe (urn+around time

amount of time to execute a particular process

educe 4aiting time amount of time in the ready 1ueue before alloted cpu time

educe esponse time Amount of time from re1uest until the first response


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#P$ Scheduling Algorithms

' categories of #P$ Scheduling algorithms

5on Preemptive algorithm

once the process is in the running state0 itwill continue until the halted state&

Preemptive algorithm currently running process may be interrupted

and moved to the ready state even if the total

burst time has not been consumed&


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#P$ Scheduling Evaluation

6antt chart 7 shows execution pattern

(urn+around (ime

4aiting (ime

#P$ $tilization


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#P$ Scheduling algorithms

%irst #ome %irst Serve ,%#%S.

Shortest 8ob %irst ,S8%.

5on+Preemptive Priority ,5PP.

Preemptive Priority ,PP.

Shortest emaining (ime %irst ,S(%. ound obin ,.


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Problem 9

Job Arrival Time Burst Time Priority

89 : 93 ;

8' 3 < 3

83 = ; 9

8< 9? @ '


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%irst #ome %irst Serve

also known as first in0 first out ,fifo.

allocates processor based on time of arrival

very simple implementation

low overhead

waiting time depends on arrival order0 exhibits

convoy effect

possible long wait for -obs that arrived later ,poor

performance.


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Shortest 8ob %irst

allocates processor based on the shortest cpu burst

ready 1ueue is treated as a priority 1ueue based on smallest

time re1uirement

also called shortest -ob next ,s-n. uses fcfs if -obs are of the same length of burst

moving shorter -obs before longer -obs improves waiting time

of short -obs more than it harms waiting time of long -obs&

optimal with regard to turn+around and waiting time

not practical0 cannot predict future cpu burst time

long -obs may never be scheduled0 thus starvation occurs


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Priority algorithm

sometimes called highest priority first ,hpf.

each -ob is assigned a priority where -obs are

scheduled based on the highest priority

static priority will work well for real time slice while

dynamic priority will work well for general workload&

high priority -obs will be processed first

there is a possibility that low priority -obs will starve&


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Shortest emaining (ime %irst

also called shortest time to completion

,stcf.

allocates processor based on theshortest remaining burst and pre+

empting if a shorter burst is found in

the ready 1ueue


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ound obin

allocates the processor based on a given time slice or

1uantum&

treats the ready 1ueue as a circular 1ueue wherein

arriving -obs or -obs preempted are placed on the tail

of the 1ueue&

simple0 low overhead0 work for interactive -obs

-ob gets fair share of cpu

shortest -ob finishes more 1uickly

poor average waiting time with similar -ob lengths

performance depends on length of time slice

higher overhead


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Problem '

ProcessArrivalTime

BurstTime

Priority

A : ; 3 > = '

# > 3 ;

) = @ 9

E 9: >

ProcessArrivalTime

BurstTime

Priority

A : 9: ; 7 3 1

# 5 8 2

) 2 4 1

E 3 9 3


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Problem ?

Job Arrival Time Burst Time Priority

A : 99 ; '

# 9= 9 3

) 3< @ ;

E > 9< 9

% 9; 93 >

6 '> 99 3

B < ' '

3: > 9


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MULTILEVEL QUEUE SCHEDULI! AL!"#ITHM


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MULTILEVEL QUEUE SCHEDULI! AL!"#ITHM

A process is assigned a 1ueue level based on memory size0

process priority or process type&

Each level has its own defined scheduling algorithm&

(he order of processing in between 1ueue levels may bebased onC

priority using either non pre+emptive or pre+emptive policy&

*ower 1ueue levels will only be able to run when all the

higher level 1ueues are empty&

Duantum or time slice where 1ueue levels are given specifiedtime slice in the central processing unit


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MULTILEVEL $EEDBAC% QUEUE &M$Q'


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MULTILEVEL $EEDBAC% QUEUE &M$Q'

(he number of 1ueues should be defined&

Each 1ueue has a defined scheduling algorithm

used

(here must be a policy used to decide when to

move up a process

(here must be a policy used to decide when to

move down a process

(here must be a policy used to decide in what

1ueue a process will enter when it needs service&


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P"*E/ =

D: *"4 S8%

D9 B6B %#%S

Process

Arrival

Time

Queue

LevelBurst Time

P9 : D:


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Problem @

*EE* : DF '

*EE* 9 DF ;

*EE* ' S8%

ProcessArrivalTime

Burst Time

A : 99

> 9>

% 9; 93

6 '> 9:

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-Process Management Ppt