Highest response ratio next

Highest Response Ratio Next (HRRN) scheduling is a non-preemptive discipline, similar to Shortest Job Next (SJN), in which the priority of each job is dependent on its estimated run time, and also the amount of time it has spent waiting. Jobs gain higher priority the longer they wait, which prevents indefinite postponement (process starvation). In fact, the jobs that have spent a long time waiting compete against those estimated to have short run times.

$Priority = \frac{waiting\ time + estimated\ run\ time}{estimated\ run\ time} = 1 + \frac{waiting\ time}{estimated\ run\ time}$

Developed by Brinch Hansen to correct certain weaknesses in SJN including the difficulty in estimating run time.

References

• William Stallings: Operating systems: internals and design principles. 4th ed., Prentice-Hall, 2001, ISBN 0-13-031999-6.