chapter 9 - uniprocessor scheduling

Question 1

What is the goal of scheduling?

Answer 1

execute processes in a way to meet system objectives like response time, throughput, and processor efficiency

Question 2

what are the types of scheduling?

Answer 2

long-term, medium-term, short-term

Question 3

what is long-term scheduling?

Answer 3

determines which programs to admit to the system (to the ready queue). controls the degree of multiprogramming

Question 4

what are the 2 decisions of long-term scheduling?

Answer 4

1. whether to admit a new process to the system
2. which process to admit

Question 5

what is medium-term scheduling?

Answer 5

once processes are admitted, the degree of multiprogramming can be further managed by this scheduler.

blocked processes can be swapped out of memory to make room for other processes in order to increase CPU utilization

processes can be activated when CPU is underutilized

Question 6

what is short-term scheduling?

Answer 6

determines which process is going to run next.

Question 7

what is another name for short-term scheduling?

Answer 7

the dispatcher

Question 8

what events is the dispatcher invoked on that may lead to choosing another process for execution?

Answer 8

clock interrupts
i/o interrupts
os calls and traps
signals

Question 9

what is the short-term scheduling criteria?

Answer 9

user oriented, performance related
user oriented, other
system oriented, performance related
system oriented, other

Question 10

what is user-oriented criteria (short-term scheduling)?

Answer 10

things the user sees

Question 11

what is system-oriented criteria (short-term scheduling)?

Answer 11

system concerns

Question 12

what is performance-related criteria (short-term scheduling)?

Answer 12

quantitative

Question 13

what is user oriented, performance related criteria?

Answer 13

turnaround time - time between submission and completion

response time - time between request and response

deadlines - process completion deadlines

Question 14

what is user oriented, other (not performance related) criteria?

Answer 14

predictability - execution time not affected by system load

Question 15

what is system oriented, performance related criteria?

Answer 15

Throughput: number of processes completed per unit of time.

Processor utilization: percent of time processor is busy.

Question 16

what is system oriented, other (not performance related) criteria?

Answer 16

Fairness: processes treated same, no starvation.

Enforcing priorities: favor high-priority processes.

Balancing resources: keep resources busy.

Question 17

what are the short-term scheduler’s scheduling policies?

Answer 17

selection function: decides which process runs next

decision mode: specifies when to run the selection function

Question 18

what are the 2 approaches in the decision mode (short-term scheduler policy)

Answer 18

Non-preemptive: runs until it terminates or is blocked

Preemptive: moves between running and ready queue, such as when a timeout occurs. Prevents one process from monopolizing the CPU.

Question 19

what are the 6 scheduling algorithms?

Answer 19

First-come-first-served
Round-robin
Shortest process next
Shortest remaining time
Highest response ratio next
Feedback

Question 20

which scheduling algos are non-preemptive?

Answer 20

FCFS, shortest process next, highest response ratio next

Question 21

which scheduling algos are preemptive?

Answer 21

round robin, shortest remaining time, feedback

Question 22

what is the effect of the first come, first serve algorithm?

Answer 22

penalizes short and I/O bound processes

Question 23

what is the effect of the round robin algorithm?

Answer 23

fair treatment

Question 24

what is the effect of the shortest process next algorithm?

Answer 24

penalizes long processes

Question 25

what is the effect of the shortest remaining time algorithm?

Answer 25

penalizes long processes

Question 26

what is the effect of the highest response ratio next algorithm?

Answer 26

good balance

Question 27

what is the effect of the feedback algorithm?

Answer 27

favors I/O bound and short processes

Question 28

which scheduling algorithms can have starvation?

Answer 28

shortest process next, shortest remaining time, feedback