Highest Response Next Scheduling

Highest response next (HRN)
HRN drives a dynamic priority value based on the estimated run time and waiting time.

The priority for each process is calculated from:

Priority (P) = (waiting time + run time) / run time

The process with the highest value will be selected for running. Value processes first appear in the ready queue, then the waiting time will be zero and hence P will be equal to 1, for all the process. After a short period of waiting however the shorter job will be favored. Consider two jobs P & Q with run time 10 and 50 after waited 5 minutes their respective priority.

P              :            p = (5+10)/10    = 1.5

Q             :            p= (5+50) /50 =   1.1

As the time pass, the wait time will become more significant, if Q has been waiting for 30 min

Q    :    p= (30+50) / 50 =1.6

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