Limited - preemptive fixed priority scheduling of real - time tasks on multiprocessors

Acknowledgement I would like to express my sincere acknowledgements to the Mälardalen University and East China University of Science and Technology for the precious chance they have provided to realize and complete my one year study here with my total satisfaction. Special appreciation goes to Dr. Radu Dobrin, Dr. Moris Behnam, Abhilash Thekkilakattil for giving me all the support that I needed during the realization of this work and their wise advises. To my friends, Kaiqian Zhu, Lingjian Gan and Xiaosha Zha who give me their honest friendship and all the help in my living here. To my family which unconditional love has been my company through this time and especially to my mother who sacrificed a lot in order to see me succeed. Abstract Real-time systems have been employed in many devices, such as automobiles, airplanes, and telephone networks. In these systems, there is a need for higher performance to handle more and more complex tasks, which single core processors cannot satisfy because of the infeasibility of further increasing processor speeds. Consequently, the interest turned to multicore systems in which the performance is improved using more number of cores/processors. Traditionally, research in real-time scheduling has focused on the two principal approaches of preemptive and non-preemptive scheduling. Preemptive scheduling typically imply prohibitively high preemption related overheads and non-preemptive scheduling can increase blocking on higher priority tasks, leading to unschedulability. Therefore, limited preemptive scheduling, in which preemptions are restricted using various mechanisms was proposed. However, scheduling real-time tasks limited preemptively complicates the scheduling problem on multiprocessors, unlike in the case of uniprocessors, because of the possibility of preempting any of the running lower priority tasks. Here, the scheduler can wait to preempt the lowest priority running task, referred to as Adaptive Deferred Scheduling (ADS), or preempt the first among the lower priority tasks that finishes executing a non-preemptive region, referred to as Regular Deferred Scheduling (RDS). In this thesis, we perform an empirical comparison of RDS and ADS using synthetically generated tasksets. For this we use well established methods for task generation along with a simulation tool that we developed. We 1) investigated the number of preemptions under RDS and ADS, as well as compared it against the number of preemptions under a fully preemptive scheduler 2) compared RDS, ADS and fully preemptive and non-preemptive scheduling using schedulability ratio by varying different task parameters. We found that the number of preemptions …