Shortest job next
Shortest job next (SJN), also known as shortest job first (SJF) or shortest process next (SPN), is a
Shortest job next is advantageous because of its simplicity and because it minimizes the average amount of time each process has to wait until its execution is complete. However, it has the potential for
Another disadvantage of using shortest job next is that the total execution time of a job must be known before execution. While it is impossible to predict execution time perfectly, several methods can be used to estimate it, such as a weighted average of previous execution times.[3] Multilevel feedback queue can also be used to approximate SJN without the need for the total execution time oracle.[1]
Shortest job next can be effectively used with interactive processes which generally follow a pattern of alternating between waiting for a command and executing it. If the execution burst of a process is regarded as a separate "job", the past behaviour can indicate which process to run next, based on an estimate of its running time.
Shortest job next is used in specialized environments where accurate estimates of running time are available.
Weighted shortest job first
Weighted shortest job first (WSJF) is a modification of the concept used in
Value-flow rate (VFR) is an alternate, more intuitive name given to WSJF which expresses cost of delay and duration using unitless relative "points" rather than actual units of time or money.[5]
See also
References
- ^ a b Arpaci-Dusseau, Remzi H.; Arpaci-Dusseau, Andrea C. (2014), Operating Systems: Three Easy Pieces [Chapter Scheduling Introduction] (PDF), Arpaci-Dusseau Books
- ISBN 978-0-13-600663-3.
- ISBN 0-471-69466-5.
- ISBN 978-1-935401-00-1.
- ^ Knesek, Doug. "'Value-Flow Rate': A Better Name for a Great Measure". Retrieved April 8, 2016.