Shortest remaining time

Shortest remaining time is a method of CPU scheduling that is a preemptive version of shortest job next scheduling. In this scheduling algorithm, the process with the smallest amount of time remaining until completion is selected to execute. Since the currently executing process is the one with the shortest amount of time remaining by definition, and since that time should only reduce as execution progresses, processes will always run until they complete or a new process is added that requires a smaller amount of time.

Shortest remaining time is advantageous because short processes are handled very quickly. The system also requires very little overhead since it only makes a decision when a process completes or a new process is added, and when a new process is added the algorithm only needs to compare the currently executing process with the new process, ignoring all other processes currently waiting to execute. However, it has the potential for process starvation for processes which will require a long time to complete if short processes are continually added, though this threat can be minimal when process times follow a heavy-tailed distribution. [http://portal.acm.org/ft_gateway.cfm?id=762486&type=pdf&coll=ACM&dl=ACM&CFID=70737957&CFTOKEN=89892650]

Like shortest job next scheduling, shortest remaining time scheduling is rarely used outside of specialized environments because it requires accurate estimations of the runtime of all processes that are waiting to execute.

ee also

*Scheduling

It doesn't use RR if two processes are of the same length because of overhead space.