A Hybrid Priority Multiprocessor Scheduling Algorithm

We propose a hybrid scheduling algorithm using deferred preemption with an online adjustment. Our approach is to prevent jobs from preempting one another until they have been promoted. We use the tasks’ Worst Case Response Time (WCRT) to determine when a promotion must occur in order to ensure safe execution. During execution, this promotion time is adjusted to extend nonpreemptive execution of lower priority tasks whenever possible. Promoted tasks have the higher priority and are scheduled using a fixed-priority scheduling algorithm. Scheduling decisions for non-promoted tasks are more flexible. We consider four strategies for determining which task to preempt: fixedpriority, maximum remaining execution time, least laxity and latest promotion time. Experimental results demonstrate that these strategies successfully avoid most preemptions compared to standard fixed-priority scheduling.