Cmpt 300 Final Exam 1

Front 1

Define scheduling

Back 1

The method by which threads, processes or data flows are given access to system resources.

Front 2

3 transition states

Back 2

1. Ready

2. Running

3. Waiting

Front 3

Why a process makes a transition?

Back 3

1. an action of the process

(non-preemptive scheduling)

2. occurrence of an external event

(preemptive scheduling)

Front 4

When will a process be selected by the processor?

Back 4

1. be in memory

2. Ready state

3. scheduled to be next

Front 5

State transition diagram

Back 5

Front 6

3 process schedulers

Back 6

1. (long term) deciding on which jobs or processes are to be admitted into the ready queue (main memory)

2. (medium term) the temporary removal of processes from main memory into secondary memory (hard disk) or vice versa

3. (short term) the actual CPU scheduler, that decides which of the ready, in memory processes are to be executed (allocated a CPU) next, following a clock interrupt, an IO interrupt, an operating system call or another form of signal

Front 7

4 types of scheduling

Back 7

1. long term scheduling

2. medium term scheduling

3. short term scheduling

4. IO scheduling

Front 8

Define long term scheduling

Back 8

the decision to add to the pool of processes to be executed

Front 9

Define medium term scheduling

Back 9

the decision to add to the number of processes that are partially or fully in main memory

Front 10

Define short term scheduling

Back 10

the decision as to which available process will be executed by the processor

Front 11

Define IO scheduling

Back 11

the decision as to which process's pending IO request shall be handled by an available IO device

Front 12

Define Scheduler Dispatcher

Back 12

the module that gives control of the CPU to the process selected by the short term dispatcher

Front 13

what should the function involving the scheduler dispatcher do?

Back 13

1. Switching context

2. Switching to user mode

3. Jumping to the proper location in the user program to restart the program

Front 14

Define dispatch latency

Back 14

the time it takes for the dispatcher to stop one process and start another

Front 15

Scheduled vs Dispatcher

Back 15

the scheduler picks process for the ready queue while the dispatcher is the modulenthay actually places the process on the processor.

there is a dispatcher for every processor on a system

Front 16

Scheduling and Process State

Back 16

new to ready/suspend is long term scheduling

ready/suspend to ready is medium term scheduling

ready to running is short term scheduling

blocked/suspend to ready is medium term scheduling

Front 17

2 types of scheduling queue

Back 17

1. Ready queue

2. device queue

Front 18

what happens during queue?

Back 18

a newly arrives process is put into the ready queue. processes wait in the ready queue for allocating the CPU. once the CPU is assigned a process then it will execute. when it executes something will happen:

1. process could issue an IO request and then it would be placed in the IO queue

2. process can create sub process and will wait for termination

3. forcibly removed from CPU due to interrupt and placed back in the ready queue

4. used too much time and put back in ready queue

Front 19

processes are created under 4 conditions (long term scheduling)

Back 19

1. new batch job

2. interactive logon

3. creation by OS to provide service

4. spawning by existing process

Front 20

once a process is created to execute a program it is in which state?

Back 20

new state

Front 21

Primary objective of the job scheduler

Back 21

provide a balance mix of jobs, such as IO bound and processor bound. It also controls the degree of multiprogramming.

Front 22

what is the degree of multiprogramming?

Back 22

if the degree of multiprogramming is stable then the average rate of process creation must be equal to the average departure rate of processes leaving the system.

Front 23

which state changes does the medium term scheduler control?

Back 23

1. Ready suspend to ready

2. Ready blocked to blocked

Front 24

the ready suspend state involves swapping between?

Back 24

main memory and mass storage

Front 25

The medium term scheduling reduces what?

Back 25

The degree of multiprogramming

Front 26

Main objective of the short term scheduler?

Back 26

increase system performance

Front 27

short term scheduler changes which process state?

Back 27

from ready to running

Front 28

what is another name for the short term scheduler?

Back 28

CPU scheduler

Front 29

what does the CPU scheduler do?

Back 29

1. selects the process among the processes that are ready to execute and allocates CPU to one of them

2. it executes most frequently and makes the fine grained decision of which process to execute next

Front 30

when is the short term scheduler invoked?

Back 30

1. when an event occurs that may lead to the blocking of the current process or that may provide an opportunity to preempt a current running process in favor of another

Front 31

In addition to changing the state from ready to running, the short term scheduler also changes what states?

Back 31

1. running to block for event wait

2. running to ready from time interrupts

3. blocked to ready as event occurs

Front 32

comparing schedulers

Back 32

long term = job scheduler

- controls degree of multiprogramming

- selects processes from the pool and loads them into memory for execution

short term = course scheduler

- less control over degree of programming

- chooses which program to execute

MED term = process swapping scheduler

- reduces the degree of multiprogramming

- re introduce the process into memory and execution can be continued

Front 33

3 Process scheduling policies of the CPU scheduler

Back 33

1. turnaround time - time between submission and completion of a process

2. response time - time from submission of a request until the response begins to be received

3. deadlines - maximize percentage of deadlines met

Front 34

Define non preemptive

Back 34

- once a process is in the running state, it will continue until it terminates or blocks itself for IO

Front 35

Define preemptive

Back 35

- currently running process may be interrupted and moved to ready state by the OS

- preemptive may occur when new process arrives, or on an interrupt

Front 36

6 scheduling policies

Back 36

1. first come first served

2. round robin

3. shortest process next

4. shortest remaining time

5. highest response ratio next

6. feedback

Front 37

Define "shortest remaining time" scheduling policy

Back 37

premptive

the one with the shortest remaining time left until completion is selected to be executed

Front 38

Define "highest response ratio next" scheduling policy

Back 38

non preemptive

dependant on estimated run time and also the amount of time it has spent waiting

Front 39

Define "feedback" scheduling policy

Back 39

if we have no indication of relative length then spn, srt, and hrrn can't be used. this one does not focus on time remain in to execute but focuses on time it has spent executing already

Front 40

Preemptive or Non premptive

Back 40

1. FCFS - nonpremptive

2. round robin - preemptive (at time quantum)

3. SPN- non preemptive

4. SRT - preemptive (at arrival)

5. HRRN - non preemptive

6. feedback - preemptive (at time quantum)

Front 41

FCFS aka FIFO advantages

Back 41

1. good for long processes

2. favor processing bound over IO bound processes

Front 42

Scheduling Algorithm Goals

Back 42

All systems

1. fairness

2. policy enforment

3. balance

Batch system

1. throughput

2. turnaround time

3. CPU utilization

Interactive system

1. response time

2. proportionality

real time system

1. meeting deadlines

2. predictability

Front 43

what part of the goals is the scheduler concerned mainly with?

Back 43

1. throughput - number of processes that complete their execution per time unit

2. latency -

turnaround - total time between submission of a process and completion

response time - time before request was submit and when the first response produced

3. fairness/waiting time

Front 44

which scheduling policy for batch systems

Back 44

1. first come first served

2. shortest job first

3. shortest remaining time next

Front 45

Scheduling for interactive systems

Back 45

1. round robin

2. priority scheduling

3. multiple queues

4. shortest process next

Front 46

what is priority Scheduling?

Back 46

CPU allocated to the process with the highest priority

Front 47

problem with priority scheduling

Back 47

Starvation

Front 48

how to prevent starvation

Back 48

aging. adds age factor which increases the priority