I had a misunderstanding earlier that every task should be treated as a periodic task. The reason for this was that I often saw people, before designing a system, first decide the deadlines for each task. So I assumed that every task must be periodic in order to meet its deadline.
But now, I feel that this is not the right way to think about RTOS system design. Instead, we should first understand the nature of each task whether it is periodic, event-driven, or interrupt-driven and then design the system accordingly.
From discussion with you, I have learned that choosing the correct type of task is more important than assuming everything is periodic.
I hope I am now moving in the right direction.