【OS】Process Scheduling Algorithm

E1.

answer.

• No attention, FCFS and non-preemptive SJF, who can be wrong

• Need to pay attention to each point in time, there may be a process with a shorter execution time preempting the current process, such as 4 s 4s in the figure$At\; 4s$ , the execution time of process B is 5s, and the execution time of process C that just arrived is 4s, so it will preempt

• HRRN-Highest Response Ratio Next, note that it is not preemptive, the time point for calculating the priority is when a process is completed. The priority calculation method is: $P=Wait/Need\; is$ the ratio of the waiting time to the required service time,$The$ higher the$P,\; the$ higher the priority

• When there is a new arrival process A and enqueue process B at a certain point in time, A joins the team before B

• When each process is processed for the first time, it will be added to the highest priority queue
• Only when the high priority queue is empty, the low priority queue will be processed, but you need to pay attention to preemption and non-preemption
• No matter which priority the queue is, it will be degraded if it is not completed within a time slice

• In the case of preemption, when a new process arrives in the high priority queue, it will directly preempt the running process in the low priority queue.
• Degradation will not occur if preempted. Degradation only occurs for those processes that have not finished running within a time slice.

standard answer.

The standard answer comes from teacher Zheng Meiguang, Central South University

E2.

• Priority scheduling algorithms are also divided into preemptive/non-preemptive types, which are not very complicated. SJF algorithm can be regarded as a special case of priority scheduling algorithms.

About the multi-level feedback queue MFQ.

【Grand Summoning】