Explain Process scheduling

Process scheduling consists of the subsequent sub-functions:

1.      Scheduling : Selects the process to be implement next on the CPU

2.      Dispatching: Sets up implementation of the selected process on the CPU

3.      Context save: Saves the status of the running process when its implementation is to be suspended

The scheduling function utilizes information from the PCB's and selects a process based on the scheduling policy in force. Dispatching engrosses the setting up of the execution environment of the selected process and loading information from the PSR and register fields of the PSB into the CPU. The context save function carries out housekeeping when a process releases the CPU or is pre-empted. It engrosses saving the PSR and registers in the appropriate fields of the PCB and changing the process state. In practice this function is performed through the interrupt processing module

The same as shown in the following fig, appearance of an event invokes the context save function. The kernel at this instant processes the event which has occurred. This processing may escort to a change of state for some process. The scheduling function is now appeal to select a process for execution on the CPU. The dispatching function arranges the implementation of the selected function on the CPU.