Algorithm for "operating system" job scheduling

First come first service scheduling algorithm (FCFS)

FCFS is the simplest scheduling algorithm, which can be used for job scheduling as well as for process scheduling.
The length of the job wait is its priority

• Dispatch according to the order in which the job arrives successively
• It could be the longest waiting job in the system.

Short Job priority scheduling algorithm (SJF)

Due to the fact that the short work process accounted for a large proportion, in order to enable them to perform longer than the long operation, and produced a short job scheduling algorithm
The length of the job is its priority

• The shorter the job, the higher the priority
• Dispatch short job first, wait for short job dispatch, then dispatch long operation

Disadvantages:

• Must know the running time of the predicted job
• Very bad for long work
• Human-machine cannot achieve interaction
• Do not fully consider the urgency of the operation, there is no guarantee that urgent work can be timely treatment

Priority scheduling algorithm (PSA)

Scheduling based on priority, externally assigned to job priority

Priority scheduling algorithm with high response ratio (HRRN)

The priority scheduling algorithm for high response ratio is to consider both the running time of the job and the waiting time of the job.

Realize:
Set a dynamic priority for each job, so that he increases with the waiting time, wait for a certain time, there must be time to get the processor
Priority = (wait time + service time required)/(time required for service)

Priority ratio:
R (P) = (response time)/time required for service

Algorithm for "operating system" job scheduling