Briefly discuss on real-time scheduling?

It is divided into two types. 

Hard real-time systems are needed to complete a critical task within a guaranteed amount of time. The scheduler then either admits the process, guaranteeing that the process will complete on time, or rejects the request as impossible.

This is called as resource reservation. Thus, hard real-time systems are composed of special-purpose software running on hardware devoted to their critical process.

Software real-time computing is less restrictive. It needs that critical processes receive priority over less fortune ones.

There are various ways to achieve preemptible to keep dispatch latency low. One is to insert preemption points in long-duration system calls that check to see while a high priority process requires to run. Another method for dealing with preemption is to make the whole kernel preemptible.