Scheduling

Question 1

What is long term scheduling?

Answer 1

decides when a process should enter the ready state to start competing for cpu

Question 2

what is short term scheduling?

Answer 2

decides which of the ready processes should run next on the cpu

Question 3

what is “real time in system” in terms of short term scheduling?

Answer 3

the total time since a process has entered the ready list

Question 4

which form of scheduling to arrival and departure times play a role?

Answer 4

long term

Question 5

what is a batch process?

Answer 5

performs longish running repetitive tasks without human intervention, like payroll processing on a certain day of the month

Question 6

what is average turnaround time?

Answer 6

average over a set of processes arrival and departure times

Question 7

in a very large process queue, Round Robin scheduling can look like __________

Answer 7

FIFO

Question 8

what is multilevel scheduling?

Answer 8

when there are separate queues that hold PRIORITY…the higher queues execute with higher priority. inside of each queue round robin is used

Question 9

what is a real time process?

Answer 9

a process that is characterized by continual input. something like video or audio and the computer MUST respond to and handle this

Question 10

what is rate monotonic algorithm?

Answer 10

schedules processes according to “period” which is to say, the process with the highest frequency of running gets prioritized highest (is preemptive)

Question 11

what is earliest deadline first algorithm?

Answer 11

schedules task according to the deadline of the task. the closer the deadline the higher priority (is preemptive)

Question 12

what is the difference between asymmetric multiprocessing and symmetric multiprocessing?

Answer 12

in asymmetric, 1 CPU handles all the scheduling, I/O and other things while the other CPUs execute only user code. but in a symmetric setup, they all split the load equally

Question 13

what is memory stall?

Answer 13

the time a CPU takes waiting for memory/data to become available

Question 14

how do multithreaded cores solve memory stall?

Answer 14

while one thread is waiting for memory, the other can continue processing

Question 15

what is push and pull migration?

Answer 15

a form of load balancing. push means that a task checks the processor load and redistributes to other CPUs…whereas pull means a CPU core may go get tasks to process if it’s queue is empty

Question 16

what is processor affinity?

Answer 16

when a process relies on cache on a specific CPU and thus due to the cost of invalidating the cache generally stays running on the same CPU

Question 17

what is the difference between coarse-grained and fine-grained hardware multithreading?

Answer 17

course-grained: threads execute until a long-latency event occurs like memory lookup

fine grained: fine-grained makes the switch much more regularly

Question 18

what is the difference between hard and soft affinity?

Answer 18

hard affinity means that the OS guarantees that the process will not change CPUs…soft affinity makes no guarantees

Question 19

what is the difference between hard and soft real time systems?

Answer 19

soft provides no guarantee for critical real time processes whereas hard does

Question 20

what is admission-control?

Answer 20

the scheduler may not even allow a process to start if it cannot guranatee that it will be completed by it’s deadline

Question 21

In Little’s formula, λ, represents the ____.

Answer 21

average arrival rate for new processes in the queue