CPU scheduling

Question 1

What are the types of scheduling? And which one is meant for CPU?

Answer 1

① long term scheduling: - keep ready to run processes on disk storage and load them into memory as needed
- long term scheduler decides which process to be loaded into main memory.
_ controls maximum of number processes that be can run in a time shared fashion.
② short term scheduling ( cpu) → select a process from a ready queue and allocates CPU
You executes much more frequently when compared to long term.

Question 2

What are the two queues that The processes move between during their life cycle?

Answer 2

① ready queue → processes that are in ready state. ② wait → processes that are blocked or waiting for io or interrupts

Question 3

Does a typical process consists of cycles of CPU execution and IO?

Answer 3

True load; add, read, write (CPU bursts) then io bursts

Question 4

What kind of bound does processes here?

Answer 4

① CPU bound ②IO bound

Question 5

What is the difference between CPU and IO bound processes?

Answer 5

CPU bound processes have long CPU bursts while io bound have short CPU bursts

Question 6

What is the impact of IO and CPU borne processes on long term and short term scheduling?

Answer 6

• Long term scheduler should select a good mix of IO and CPU bound processes
• ensures that both ready queues and wait queues are balanced and not empty.

Question 7

What is the difference between preemptive and non preemptive scheduling?

Answer 7

① non-preemptive → each running process keeps the CPU until
- it completes
Or switches to the waiting state preemptive
② preemptive → a process might be forced to release CPU even though it is neither completed or blocked
This happens when in time sharing systems when the running process reaches the end of its time slice.

Question 8

What metrics can be used to compare different scheduling polices.?

Answer 8

① CPU Utilization → percentage of time CPU is busy executing jobs.
② Turnaround time TA → amont of time to execute a particular process.
③ wait time → amount of time a process can wait in the ready queue
④ Response time → amount of time it takes from when a request is submits and the first response it produced,not the complete output.

Question 9

TA formula

Answer 9

TA = T(COMPLETION) - T (arrival)

Question 10

Waiting time formula Tw

Answer 10

Tw = TA -T ( cpu time size)

Question 11

Response time formula

Answer 11

Tr = T ( start execution ) - T ( arrival)

Question 12

What is FCFS

Answer 12

Process that arrives first runs first. FIFO

Question 13

What is convoy effect?

Answer 13

Number of relatively short processes get queues behind a heavy weight process

Question 14

What is shortest job first scheduling?SJF

Answer 14

The CPU is assigner to the process with the smallest next CPU time

Question 15

What are the scheme of SJF?

Answer 15

• Non-preemptive
• preemptive → Shortest time to completion first STCF

Question 16

When is non preemptive SJF optimal?

Answer 16

① if all the processes are ready simultaneously
② gives minimum average waiting time for a given set of processes.

Question 17

When is preemptive SJF is optimal?

Answer 17

Thank it processes May arrive at different times however they have poor response time

Question 18

When is response time optimal?

Answer 18

Response time is optimal with round Robin but it has worst turnround time