Highest Response Ratio Next

Highest Response Ratio Next (HRRN) is a non-preemptive scheduling method that always assigns the process with the highest response ratio to the processor . This quotient is calculated as follows:

${\displaystyle ResponseRatio={\frac {Laufzeit+Wartezeit}{Laufzeit}}}$

Note: The times to be used are values ​​that can be estimated, as usually no sufficiently reliable statement about future behavior is possible.

The scheduler only becomes active again when the last assigned process has ended or is blocked (e.g. due to I / O operations). This scheduling algorithm prefers processes with little computing time because the ResponseRatio increases faster with increasing waiting time. It also prevents livelocks for long processes, which distinguishes it from Shortest-Remaining-Time (SRT) or Shortest-Job-First (SJF).

The formula can be simplified to:

${\displaystyle ResponseRatio={\frac {Wartezeit}{Laufzeit}}+1}$

Since the values ​​are only compared with each other by the scheduler, the 1 could just as easily be omitted.

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• William Stallings: Operating Systems: Principles and Implementation . 4th edition, Prentice-Hall, Munich 2002, ISBN 3-8273-7030-2 .