Priority Scheduling Algorithms in Operating Systems: Performance and Fairness

Explore priority scheduling algorithms in operating systems, comparing preemptive and non-preemptive approaches. This guide explains how priority levels influence CPU allocation, discusses methods for assigning priorities (static, dynamic), and analyzes the impact on system performance and fairness.

Priority Scheduling Algorithms in Operating Systems

Understanding Priority Scheduling

Priority scheduling is a CPU scheduling algorithm that assigns a priority level to each process. The operating system's scheduler then uses these priorities to determine which process gets access to the CPU next. Higher-priority processes are typically given preference over lower-priority ones, although the exact scheduling mechanism depends on whether the algorithm is preemptive or non-preemptive.

Preemptive vs. Non-Preemptive

Priority scheduling can be either preemptive or non-preemptive:

• Preemptive: A higher-priority process can interrupt (preempt) a lower-priority process that's currently using the CPU.
• Non-preemptive: A process runs to completion or until it blocks (e.g., waiting for I/O), without being interrupted by higher-priority processes.

Static vs. Dynamic Priorities

Priority can be assigned in two ways:

• Static Priority: The priority of a process is fixed when it's created and doesn't change during its execution. This is simpler to implement but might lead to starvation (where a low-priority process never gets to run).
• Dynamic Priority: The priority of a process changes over time, often based on factors like waiting time or resource usage. Dynamic priority schemes can be more complex to implement but can help prevent starvation by boosting the priority of processes that have waited a long time.