Process Scheduling

Question 1

what is a scheduler

Answer 1

decides which process to run. approach depends on the processing mode

Question 2

what processing modes are there and what scheduling approach will be taken

Answer 2

interactive- round robin

real time- minimises latency by relying on priorities. Hard and soft constraints.

batch- allow each job to complete before going on to the next

Question 3

what are the process states

Answer 3

running

ready

blocked

Question 4

what principles does a scheduler combine

Answer 4

process states

linked lists

time slicing

sleeping

Question 5

what is context switching

Answer 5

a running process is paused and evicted from the processor.

performed by the scheduler.

1. save the process registers within PCB
2. choose the new process
   for process switch only:
3. change memory management page tables and flush TLB
4. flush caches

Question 6

what types of process priority are there

Answer 6

constant and dynamic.

Question 7

what is priority inversion

Answer 7

when a high priority task is prevented from running by a low priority one

Question 8

what is sleep

Answer 8

the unix name for a blocked process, waiting for the time. queue until a timer interrupt.

Question 9

what are hard and soft requirements in real time processing

Answer 9

hard- safety critical, where failure would result in catastrophe

soft- real time requirement but not critical.

Question 10

what is different about real time scheduling

Answer 10

the policy is steered away from time slicing and towards pre-emption. ready queue stored by priority