chapter 9 - uniprocessor scheduling Flashcards
(28 cards)
What is the goal of scheduling?
execute processes in a way to meet system objectives like response time, throughput, and processor efficiency
what are the types of scheduling?
long-term, medium-term, short-term
what is long-term scheduling?
determines which programs to admit to the system (to the ready queue). controls the degree of multiprogramming
what are the 2 decisions of long-term scheduling?
- whether to admit a new process to the system
- which process to admit
what is medium-term scheduling?
once processes are admitted, the degree of multiprogramming can be further managed by this scheduler.
blocked processes can be swapped out of memory to make room for other processes in order to increase CPU utilization
processes can be activated when CPU is underutilized
what is short-term scheduling?
determines which process is going to run next.
what is another name for short-term scheduling?
the dispatcher
what events is the dispatcher invoked on that may lead to choosing another process for execution?
clock interrupts
i/o interrupts
os calls and traps
signals
what is the short-term scheduling criteria?
user oriented, performance related
user oriented, other
system oriented, performance related
system oriented, other
what is user-oriented criteria (short-term scheduling)?
things the user sees
what is system-oriented criteria (short-term scheduling)?
system concerns
what is performance-related criteria (short-term scheduling)?
quantitative
what is user oriented, performance related criteria?
turnaround time - time between submission and completion
response time - time between request and response
deadlines - process completion deadlines
what is user oriented, other (not performance related) criteria?
predictability - execution time not affected by system load
what is system oriented, performance related criteria?
Throughput: number of processes completed per unit of time.
Processor utilization: percent of time processor is busy.
what is system oriented, other (not performance related) criteria?
Fairness: processes treated same, no starvation.
Enforcing priorities: favor high-priority processes.
Balancing resources: keep resources busy.
what are the short-term scheduler’s scheduling policies?
selection function: decides which process runs next
decision mode: specifies when to run the selection function
what are the 2 approaches in the decision mode (short-term scheduler policy)
Non-preemptive: runs until it terminates or is blocked
Preemptive: moves between running and ready queue, such as when a timeout occurs. Prevents one process from monopolizing the CPU.
what are the 6 scheduling algorithms?
First-come-first-served
Round-robin
Shortest process next
Shortest remaining time
Highest response ratio next
Feedback
which scheduling algos are non-preemptive?
FCFS, shortest process next, highest response ratio next
which scheduling algos are preemptive?
round robin, shortest remaining time, feedback
what is the effect of the first come, first serve algorithm?
penalizes short and I/O bound processes
what is the effect of the round robin algorithm?
fair treatment
what is the effect of the shortest process next algorithm?
penalizes long processes
