Scheduling Metrics

operating-systems scheduling

Definition

Scheduling Metrics

Scheduling metrics are quantitative measures used to evaluate and compare scheduling strategies.

Metrics

Turnaround Time ( $T_r$)

Total time a process spends in the system, from arrival to completion.

$$T_r=T_{completion}-T_{arrival}=\text{Wait Time}+\text{Service Time}$$

Wait Time ( $w$)

Total time a process spends in the Ready Queue waiting for the CPU.

Service Time ( $s$)

Actual time the process is in the Running state executing on the processor.

Normalised Turnaround Time

Ratio of turnaround time to service time.

$$\text{Normalised }{T}_r=\frac{T_r}{s}$$

Value of 1.0 is ideal (no waiting). Higher values indicate relative delays. Useful for comparing fairness across different process lengths.

Response Ratio ( $RR$)

Used in HRRN to balance short and long-waiting processes.

$$RR=\frac{w+s}{s}$$

As wait time $w$ increases, the ratio grows, allowing long processes to eventually out-compete new short ones, preventing starvation.