Midterm Review (2021 Spring)

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University of Massachusetts Amherst 2

Homework2

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

0 5 10 15 20 25 30 35

P1 R R R R R R R w w w r r R R R

P2 r r r r r r r R R R R R w w w w w w w w R R R R R R R

b. Shortest job first

5 10 15 20 25 30 35

P1 r r r r r R R R R R R R w w w r r r r r R R R

P2 R R R R R w w w w w w w w R R R R R R R

c. Preemptive shortest job first

5 10 15 20 25 30 35

P1 r r r r r R R R R R R R w w w R R R

P2 R R R R R w w w w w w w w R R r r r R R R R R

d. Round robin with a quantum of 2

5 10 15 20 25 30 35

P1 R R r r R R r r R R r R w w w R R R

P2 r r R R r r R R r r R w w w w w w w w R R R R R R R

Algorithm

P1 WT

P2 WT

Avg WT

P1 FT

Schd Len

CPU Ut

FCFS

2

7

4.5

15

27

27 81.48%

SJF

10

0

5

23

20

23 95.65%

PSJF

5

3

4

18

23

23 95.65%

RR 2

5

6

5.5

18

26

26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst

will make RR behave like FCFS.

P1: CPU-7, IO-3, CPU-3

P2: CPU-5, IO-8, CPU-7

Kevin Zheng Tongping Liu

ECE 570: System Software Design 2 March 2021

Homework 2 1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3 P2: CPU 5, I/O 8, CPU 7 1 just before 2

a. First-come/first-served

0 5 10 15 20 25 30 35 P1 R R R R R R R w w w r r R R R P2 r r r r r r r R R R R R w w w w w w w w R R R R R R R

b. Shortest job first

5 10 15 20 25 30 35 P1 r r r r r R R R R R R R w w w r r r r r R R R P2 R R R R R w w w w w w w w R R R R R R R

c. Preemptive shortest job first

5 10 15 20 25 30 35 P1 r r r r r R R R R R R R w w w R R R P2 R R R R R w w w w w w w w R R r r r R R R R R

d. Round robin with a quantum of 2

5 10 15 20 25 30 35 P1 R R r r R R r r R R r R w w w R R R P2 r r R R r r R R r r R w w w w w w w w R R R R R R R

Algorithm P1 WT P2 WT Avg WT P1 FT P1 FT Schd Len CPU Ut FCFS 2 7 4.5 15 27 27 81.48% SJF 10 0 5 23 20 23 95.65% PSJF 5 3 4 18 23 23 95.65% RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst will make RR behave like FCFS.

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

Algorithm P1 WT P2 WT Avg WT P1 FT P1 FT Schd Len CPU Ut

FCFS 2 7 4.5 15 27 27 81.48%

SJF 10 0 5 23 20 23 95.65%

PSJF 5 3 4 18 23 23 95.65%

RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst

will make RR behave like FCFS.

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

FCFS 2 7 4.5 15 27 27 81.48%

SJF 10 0 5 23 20 23 95.65%

PSJF 5 3 4 18 23 23 95.65%

RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

(3)

Homework2

P1: CPU-7, IO-3, CPU-3

P2: CPU-5, IO-8, CPU-7

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

0 5 10 15 20 25 30 35

P1 R R R R R R R w w w r r R R R

P2 r r r r r r r R R R R R w w w w w w w w R R R R R R R

b. Shortest job first

5 10 15 20 25 30 35

P1 r r r r r R R R R R R R w w w r r r r r R R R

P2 R R R R R w w w w w w w w R R R R R R R

c. Preemptive shortest job first

5 10 15 20 25 30 35

P1 r r r r r R R R R R R R w w w R R R

P2 R R R R R w w w w w w w w R R r r r R R R R R

d. Round robin with a quantum of 2

5 10 15 20 25 30 35

P1 R R r r R R r r R R r R w w w R R R

P2 r r R R r r R R r r R w w w w w w w w R R R R R R R

Algorithm

P1 WT

P2 WT

Avg WT

P1 FT

Schd Len

CPU Ut

FCFS

2

7

4.5

15

27

27 81.48%

SJF

10

0

5

23

20

23 95.65%

PSJF

5

3

4

18

23

23 95.65%

RR 2

5

6

5.5

18

26

26 84.62%

2. agree/disagree

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

FCFS 2 7 4.5 15 27 27 81.48%

SJF 10 0 5 23 20 23 95.65%

PSJF 5 3 4 18 23 23 95.65%

RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst

will make RR behave like FCFS.

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

FCFS 2 7 4.5 15 27 27 81.48%

SJF 10 0 5 23 20 23 95.65%

PSJF 5 3 4 18 23 23 95.65%

RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst

will make RR behave like FCFS.

Kevin Zheng

Tongping Liu

ECE 570: System Software Design

2 March 2021

Homework 2

1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3

P2: CPU 5, I/O 8, CPU 7

1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

5 10 15 20 25 30 35 P1 R R r r R R r r R R r R w w w R R R P2 r r R R r r R R r r R w w w w w w w w R R R R R R R Algorithm P1 WT P2 WT Avg WT P1 FT P1 FT Schd Len CPU Ut FCFS 2 7 4.5 15 27 27 81.48% SJF 10 0 5 23 20 23 95.65% PSJF 5 3 4 18 23 23 95.65% RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU

burst first, not the shortest total execution time

b. agree – a quantum that is greater than or equal to the longest CPU burst

will make RR behave like FCFS.

Kevin Zheng Tongping Liu

ECE 570: System Software Design 2 March 2021

Homework 2 1. CPU scheduling

P1: CPU 7, I/O 3, CPU 3 P2: CPU 5, I/O 8, CPU 7 1 just before 2

a. First-come/first-served

b. Shortest job first

c. Preemptive shortest job first

d. Round robin with a quantum of 2

5 10 15 20 25 30 35 P1 R R r r R R r r R R r R w w w R R R P2 r r R R r r R R r r R w w w w w w w w R R R R R R R Algorithm P1 WT P2 WT Avg WT P1 FT P1 FT Schd Len CPU Ut FCFS 2 7 4.5 15 27 27 81.48% SJF 10 0 5 23 20 23 95.65% PSJF 5 3 4 18 23 23 95.65% RR 2 5 6 5.5 18 26 26 84.62%

2. agree/disagree

a. disagree – shortest job first scheduling runs the job with the shortest CPU burst first, not the shortest total execution time

(4)

Homework2

• Q2:

– Disagree. In SJF scheduling, the task

with the next

shortest cpu burst

,

not total execution time

, will be

scheduled first.

– Agree. There is a quantum value in RR to make it

(5)

Homework2

void initLock(bool * lock) {

*lock = false;

}

void lock(bool * lock) {

bool key = true;

while (key == true) {

swap(&key, lock);

}

void unlock(bool * lock) {

*lock = false;

(6)

Homework2

• Pros:

– Easy to implement

– No priority inversion.

– Deletion safety

• Cons:

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Midterm

• Time:

– March 17: 8pm~10PM (EST)

• Zoom Link (lectures link):

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Midterm Exam Format

• 2-hour exam over the zoom (open the video)

• Ask questions in a separate room

• Close notes but with one cheat sheet

(back-and-forth)

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Lecture-1: Overview

• Evolution of Computer Systems and OS

Concepts

• Different Types of OS

– Parallel/Distributed/Real-time/Embedded OS

• OS Services

• OS Structures and Basic Components

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Important Concepts

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Lecture-2: Process

• Programs and Processes

• Process (program image) in memory

• PCB: Process Control Block

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Important Concepts

• Difference between a program with a process

• Program states and state transition

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Lecture-3: Threads

• Motivation and thread basics

– Resource requirements: thread vs. process

• Thread implementations

– User threads: e.g., Pthreads and Java threads

– Kernel threads: e.g., Linux tasks

– Map user- and kernel-level threads

– Lightweight process and scheduler activation

• Other issues with threads:

– process creation and signals etc.

– Memory sharing model

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Important Concepts

• Difference and similarities between threads and

processes

• Pros and cons of thread models: 1-to-1, n-to-1, and

m-to-n

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Lecture-5

• Shared data access

– Race condition and critical section

– General structure for enforce critical section

• Synchronization mechanism

– Hardware supported instructions

– Software solution

• Classical Synchronization Problems

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Important Concepts

• Critical section

• General structure for ensuring safety of critical

section

• swap() and testAndset()

• Semaphore vs. Mutex

• Monitor

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Lecture-6

• Implementing Multithreaded Programs

– Synchronization Errors:

• Deadlock, race condition, order violation, atomicity violation

– Performance Issues:

• Hardware related: false/true sharing

• Software related: lock issues

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Important Concepts

• Four common synchronization errors

• False/true sharing performance issues

• Lock performance issues

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Question #1

• What is the difference between a process and a

thread?

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Question #2

• What process states for a running process is not

stored in the address space?

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Question #3

• What is the problem with defining large critical

sections in multi-threaded code?

• Results in a lot of waiting by the threads. You

want to release the lock as much as possible.

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Question #4

• When might you use signal() instead of

broadcast() with condition variables?

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Question #5

• Does the order of the signal() calls matter with

semaphores in terms of causing/preventing

deadlock? Does the order of the wait() calls

matter?

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Question #6

• Name three internal events a thread may

execute to return control back to the OS?

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Question #7

• Name the most common external event that

transfers control back to the OS from a

running thread?

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Question #8

• What are the basic steps involved with creating

a new thread?

• Allocate and initialize a new TCB, allocate a new

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Question #9

• Why is it ok for the OS to disable interrupts,

but not application programs?

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Question #10

• How does the testAndset(X) function work?

Implement a simple busy-waiting lock for

multi-processors using the testAndset(X)

function.

• lock () { while (testAndset(value) == 1) {;}

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Question #11

• What are the options for ensuring atomicity on

a uniprocessor within the OS?

• Disabling interrupts, atomic load-store,