OS Process Scheduling Q & A #4

Question: What is Highest Response Ratio Next (HRN) Scheduling?

Answer:

• HRN is non-preemptive scheduling algorithm.

• In Shortest Job First scheduling, priority is given to shortest job, which may sometimes indefinite blocking of longer job.

• HRN Scheduling is used to correct this disadvantage of SJF.

• For determining priority, not only the job's service time but the waiting time is also considered.

• In this algorithm, dynamic priorities are used instead of fixed priorities.

• Dynamic priorities in HRN are calculated as

  Priority = (waiting time + service time) / service time.

• So shorter jobs get preference over longer processes because service time appears in the denominator.

• Longer jobs that have been waiting for long period are also give favorable treatment because waiting time is considered in numerator.