Review Questions on Chapter III—Scheduling

Review Questions onChapter III—Scheduling COSC 4330/6310 Summer 2013

First Question • In the Round Robin policy, what the advantages and disadvantages of selecting a small time quantum? (2×5 points)

First Question • In the Round Robin policy, what the advantages and disadvantages of selecting a small time quantum? (2×5 points) • The main advantage of small time slices is a faster response time for interactive requests

First Question • In the Round Robin policy, what the advantages and disadvantages of selecting a small time quantum? (2×5 points) • The main advantage of small time slices is a faster response time for interactive requests • Their main disadvantage is too much CPU time taken by context switches

Second Question • Consider the following set of parameters for a System V Release 4 scheduler with four priority levels: #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 800 X 1 1000 1 # 0 400 0 2 1000 2 # 1 200 1 3 200 3 # 2 100 2 Y 200 3 # 3 • Which are the sole reasonable values for X and Y? • X=__ and Y= __

Second Question • Consider the following set of parameters for a System V Release 4 scheduler with four priority levels: #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 800 X 1 1000 1 # 0 400 0 2 1000 2 # 1 200 1 3 200 3 # 2 100 2 Y 200 3 # 3 • Which are the sole reasonable values for X and Y? • X=_0_ and Y= __

Second Question • Consider the following set of parameters for a System V Release 4 scheduler with four priority levels: #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 800 X 1 1000 1 # 0 400 0 2 1000 2 # 1 200 1 3 200 3 # 2 100 2 Y 200 3 # 3 • Which are the sole reasonable values for X and Y? • X=_0_ and Y= _3_

Third Question • Consider the following System V Release 4 scheduler: #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 800 0 1 16000 0 # 0 400 0 2 8000 2 # 1 200 2 3 4000 3 # 2 100 2 4 2000 4 # 3 • and identify the four incorrect parameters: (4×5 points)

Fourth Question • Consider the following System V Release 4 scheduler: (3×5 points) #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 1000 0 1 16000 1 # 0 500 1 2 8000 2 # 1 200 1 3 4000 3 # 2 100 2 3 2000 3 # 3 • Which events can increase the priority of a process at level 2? • Which events can lower it?

Fourth Question • Consider the following System V Release 4 scheduler: (3×5 points) #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 1000 0 1 16000 1 # 0 500 1 2 8000 2 # 1 200 1 3 4000 3 # 2 100 2 3 2000 3 # 3 • A return from the wait state or a long wait in the ready queue will increase the priority of a process

Fourth Question • Consider the following System V Release 4 scheduler: (3×5 points) #ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait LVL 1000 0 1 16000 1 # 0 500 1 2 8000 2 # 1 200 1 3 4000 3 # 2 100 2 3 2000 3 # 3 • A return from the wait state or a long wait in the ready queue will increase the priority of a process • A CPU timer interrupt will decrease it

Short Questions • What is the major limitation of theround-robin scheduling policy?

Short Questions • What is the major limitation of theround-robin scheduling policy? • RR cannot provide at the same time a good interactive response time and a good throughput at medium to heavy load

Short Questions • What is the main advantage of preemptive schedulersover non-preemptive ones?

Short Questions • What is the main advantage of preemptive schedulersover non-preemptive ones? • Scheduler can take CPU way from processes "monopolizing" the CPU • Other processes do not have to wait as long

Short Questions • What do schedulers typically do to increase the priorities of I/O-bound processes?

Short Questions • What do schedulers typically do to increase the priorities of I/O-bound processes? • They increase the priorities of processes returning to the ready queue from the wait state • Very likely to have performed an I/O

Short Questions • What do schedulers typically do to lower the priorities of CPU-bound processes?

Short Questions • What do schedulers typically do to lower the priorities of CPU-bound processes? • They decrease the priority of processes who have been preempted because they have exhausted their CPU time slice

True or False • The Round-Robin scheduling algorithm does not differentiate between CPU-bound and I/O-bound processes.

True or False • The Round-Robin scheduling algorithm does not differentiate between CPU-bound and I/O-bound processes. • TRUE because all processes have the same priority

True or False • The Round-Robin scheduling algorithm is starvation-free.

True or False • The Round-Robin scheduling algorithm is starvation-free. • TRUE because all processes have the same priority

True or False • Most schedulers adjust the priorities of real-time processes in order to give each process its fair share of the CPU.

True or False • Most schedulers adjust the priorities of real-time processes in order to give each process its fair share of the CPU. • FALSE, the schedulers we have discussed assign fixed priorities to real-time processes

True or False • Steps taken to decrease the response time of a system can sometimes decrease its throughput.

True or False • Steps taken to decrease the response time of a system can sometimes decrease its throughput. • TRUE, think of the round-robin policy

True or False • All preemptive policies have multiple priority levels.

True or False • All preemptive policies have multiple priority levels. • TRUE, think of the round-robin policy

True or False • The throughput of a computer using a round-robin scheduling policy often goes down when the number of users goes up.

True or False • The throughput of a computer using a round-robin scheduling policy often goes down when the number of users goes up. . • TRUE because the context switch overhead is likely to increase

Review Questions on Chapter III—Scheduling