Operating System test 2 chapter 5 (chapter 6 of the essentials textbook)

chapter 5

CPU utilization

keep the CPU as busy as possible

Throughput

# of processes that complete their execution per time unit

Turnaround time

amount of time to execute a particular process

Waiting time

amount of time a process has been waiting in the ready queue

response time

amount of time it takes from when a request was submitted until the first response is produced.

scheduling algorithm optimization criteria

▪ Max CPU utilization

▪ Max throughput

▪ Min turnaround time

▪ Min waiting time

▪ Min response time

FCFS (First‑Come, First‑Served)

Non‑preemptive; processes run in the order they arrive; simple but can cause long wait times (convoy effect).

SJF (Shortest Job First)

Non‑preemptive; selects the process with the shortest CPU burst; optimal for average waiting time but requires burst‑time prediction.

SRJF (Shortest Remaining Job First)

Preemptive version of SJF; always runs the process with the shortest remaining time; can interrupt running processes.

RR (Round Robin)

Preemptive; each process gets a fixed time quantum in a cycle; good for time‑sharing and fairness.

Multilevel Feedback Queue

A CPU scheduler with multiple priority queues where processes move between levels based on behavior; higher queues run first, usually with Round Robin.

Thread scheduling

determines how user‑level and kernel‑level threads are chosen to run

process-contention scope (PCS)

for user‑level threads competing within a process

system-contention scope (SCS)

for kernel threads competing across the whole system.

Symmetric multiprocessing (SMP)

where each processor is self scheduling.

Load balancing

attempts to keep workload evenly distributed

push mitigation

periodic task checks load on each processor, and if found pushes task from overloaded CPU to other CPUs

pull migration

idle processors pulls waiting task from busy processor

Soft affinity

the operating system attempts to keep a thread running on the same processor, but no guarantees.

Hard affinity

allows a process to specify a set of processors it may run on.