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CSE 430 Spring 2008 Midterm 2: CPU Scheduling & Process Coordination, Exams of Operating Systems

Arizona State University (ASU) - TempeOperating Systems

The questions and instructions for the midterm exam of cse 430: operating systems, held in spring 2008. The exam covers topics such as cpu scheduling algorithms, process coordination, and classical synchronization problems. Students are required to answer questions related to gantt charts, mutual exclusion, the dining philosophers problem, and monitor synchronization.

Typology: Exams

Pre 2010

Uploaded on 09/02/2009

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CSE 430
SPRING 2008 MIDTERM 2
(6:40 CLASS)
NAME
Put Name on Every Page
1. (30) Scheduling
Given the following jobs:
Job # Arrival Time Run Time Priority (1 is highest)
A 0 3 5
B 2 6 4
C 4 4 3
D 6 5 2
E 8 2 1
(a) (18) Draw a Gantt chart to illustrate the execution of these jobs for each of the
following 3 CPU scheduling algorithms: Shortest Remaining Time First; Preemptive
Priority and Round Robin with q=4. Make the following assumption to handle 'ties.' In
Shortest Remaining Time First, if two jobs have the same shortest remaining time, the
one that arrived first gets to go. Helpful Hint: Take your time. Be careful on SRTF and
RR.
(b) (6) What is the average waiting time for Preemptive Priority?
(c) (3) What bound does context switch time place on the quantum for Round Robin process
scheduling and why is this so?
(d) (3) Why is it essentially impossible to implement Shortest Remaining Time First?
pf3
pf4

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CSE 430

SPRING 2008

MIDTERM 2

(6:40 CLASS)

NAME

Put Name on Every Page

1. (30) Scheduling Given the following jobs: Job # Arrival Time Run Time Priority (1 is highest) A 0 3 5 B 2 6 4 C 4 4 3 D 6 5 2 E 8 2 1 (a) (18) Draw a Gantt chart to illustrate the execution of these jobs for each of the following 3 CPU scheduling algorithms: Shortest Remaining Time First; Preemptive Priority and Round Robin with q=4. Make the following assumption to handle 'ties.' In Shortest Remaining Time First, if two jobs have the same shortest remaining time, the one that arrived first gets to go. Helpful Hint : Take your time. Be careful on SRTF and RR. (b) (6) What is the average waiting time for Preemptive Priority? (c) (3) What bound does context switch time place on the quantum for Round Robin process scheduling and why is this so? (d) (3) Why is it essentially impossible to implement Shortest Remaining Time First?

CSE 430

SPRING 2008

MIDTERM 2

(6:40 CLASS)

NAME

Put Name on Every Page

2. (25 + 2 points extra credit) Process Coordination For this question use the Addendum to MT2 which contains Peterson’s solution for achieving mutual exclusion and also obtaining mutual exclusion by setting and clearing locks using a HW instruction similar to TestAndSet. (a) (8) Explain how this solution guarantees mutual exclusion. (b) (8) Explain how this solution guarantees a bounded waiting time on the selection of a given process. Include in your explanation what that bound is. (c) (9) Obtaining mutual exclusion by setting and clearing locks using a tsl register,flag instruction similar to TestAndSet as shown in the figure at the bottom of the handout clearly provides a much simpler solution to the mutual exclusion problem. It implements memory access operations in a way that we could not assume when designing a software protocol for mutual exclusion. What is different about the characteristics of the memory operations assumed in Peterson’s software protocol and the characteristics of the memory operation present in the tsl register,flag instruction. NOTE : To answer this question you need to state the particular relevant characteristic of memory operations assumed in Peterson’s protocol and the corresponding particular relevant characteristic of memory operations in the tsl register,flag instruction. (d) (2 pts. extra credit) T or F The solution using the tsl register,flag instruction also provides bounded waiting.

CSE 430

SPRING 2008

MIDTERM 2

(6:40 CLASS)

NAME

Put Name on Every Page

4. (17 + 3 points extra credit) More Process Coordination (a) (2) T or F At a higher level we have the same problems in correctly using monitors as we had with correctly using semaphores. (b) (3) Explain why disabling interrupts is not appropriate for implementing synchronization primitives in multiprocessor systems. (c) (5) Why do Solaris, Linux, and Windows 2000 use spinlocks as a synchronization mechanism only on multiprocessor systems and not on single-processor systems? (d) (7) Explain how that if the signal semaphore operation is not executed atomically, then for the case where the semaphore controls access to multiple instances of the same type (e.g., 3 printers), access to one or more of the resources could be eliminated. (e) (3 pts. extra credit) How does the signal() operation associated with monitors differ from the corresponding operation defined for semaphores?