Process Scheduling in OS (Operating System):
Operating system uses various schedulers for the process scheduling described below.
1. Long term scheduler:
The phrase "job scheduler" also applies to long-term schedulers. It picks processes from the pool (secondary memory) and retains them in the primary memory's ready queue.
The degree of multiprogramming is mostly controlled by the long-term scheduler. The goal of the long-term scheduler is to select the ideal balance of CPU- and IO-bound activities from the pool of available workloads.
The CPU will spend the majority of the time idle if the job scheduler selects more IO-bound processes, which could result in all of the jobs being blocked at all times. This will lessen Multiprogramming to some extent. As a result, the long-term scheduler's job is extremely important and could have a long-term impact on the system.
2. Short term scheduler:
CPU scheduler is another name for the short-term scheduler. From the ready queue, it chooses a job and sends it to the CPU for execution.
The work that will be assigned for execution is chosen using a scheduling method. The short-term scheduler's work can be crucial because if it chooses a job with a high CPU burst time, all subsequent jobs will have to wait in the ready queue for a very long time.
Starvation is a condition that can happen if the short-term scheduler chooses the job incorrectly.
3. Medium term scheduler:
The switched out processes are handled by the medium term scheduler.It is necessary to switch a running process from running to waiting if it requires some IO time to complete.
For this, a medium-term scheduler is employed. To make place for the other processes, it removes the process from the operating state. These processes are known as swapped out processes, and this action is referred to as switching. The processes' suspension and restart are handled by the medium-term scheduler.
The amount of multiprogramming is decreased. To have the ideal balance of processes in the ready queue, swapping is required.
