ISSN: 2455-2631 © May 2016 IJSDR | Volume 1, Issue 5 IJSDR1605010 International Journal of Scientific Development and Research (IJSDR) www.ijsdr.org 49 Comparison between EDF_RM and EDF_DM in dynamic scheduling algorithm with sporadic task Hemang Thakar Assistant Professor DJMIT engineering college Computer Science and Engineering Abstract: Real time system is divided in to two algorithms static and dynamic. Both algorithm want to complete his job in given deadline or before deadline but no one algorithm are successfully complete his job in overloaded and under loaded condition. Dynamic algorithm able to give optimal result in under-loaded condition but not able to give same result in over-loaded condition. Static algorithm not able to give optimal result in under-loaded condition but able to perform well in over-loaded condition. So we think new algorithm to give result optimum in under-loaded condition and give high result in over-loaded condition. We are thinking to mix up dynamic scheduling algorithm EDF (Earlier dead line first) and static scheduling algorithm DM (dead line monotonic). EDF algorithm give optimal result in under-loaded condition and DM algorithm perform well in over-loaded condition. In this paper we compare EDF_RM and EDF_DM algorithm. Here EDF_RM is better than EDF_DM. Keywords: EDF, LLF, RM, DM, Scheduling Algorithms, Real-Time operating Systems. I. Introduction Real-time systems have well defined, fixed time constraints. Two types of real-time system available hard and soft. Where hard real time system work on principal job must complete their execution before deadline. It’s useful where missing deadline may be serious consideration. Soft real time system is more flexible which allow job to execution beyond the deadline. It’s applicable where cost of job is more important than can sequences of missing deadline. a. Real-Time Scheduler Generally it’s worked in two categories static and dynamic. In case of static algorithm its applied priorities at initial (design) level and remain same throughout the task. In case of dynamic algorithm priority assign on runtime which depended on parameters of task. We can make dynamic scheduling with static priority where Rate Monotonic (RM) and Deadline Monotonic (DM) are two examples of its and Earliest Deadline First (EDF) and Least laxity (Slack) time First (LLF) are belongs to dynamic scheduling with dynamic priority. Here in dynamic priority algorithm are implements in categories first. In which job to change priority daring it is activation and in another type job cannot able to change priority. EDF is job level fixed priority algorithm of this category. Another side job can change priority during execution called job level dynamic-priority algorithm. Least laxity (slack) time algorithm belongs to it. At time t, the slack time of a job is (d - t), where d is the jobs deadline and t is its remaining execution requirement. Here, the slack time is the maximum amount of time a job may be forced to wait if it were to execute on a processor and still meet its deadline. The LSF algorithms give higher priority to jobs with smaller slack time. Since the slack time of a job can change over time, the job priorities can change dynamically. II. The Scheduling Algorithm a. EDF Scheduling Algorithm EDF Scheduling Algorithm is called earliest dead line first or nearest deadline first Scheduling Algorithm. EDF is dynamic Scheduling algorithm. The task with the earliest deadline has the highest priority [1]. EDF Scheduling Algorithm gives 100% task utilization when system is in under loaded situation or U<=1 But when task utilization cross load factor more then 1 or slightly overloaded processor utilization decreases exponentially [4]. b. RM Scheduling Algorithm RM Scheduling Algorithm is called Rate Monotonic Algorithm.RM is a fixed or static priority scheduling algorithm. RM assigns priorities to tasks based on their periods [4]. Disadvantage of this algorithm is that they are not give 100% result in under loaded situation [6]. RM gives better performance in over loaded situation as compare to dynamic scheduling. In RM algorithm shortest period gives first chances to execute but when more than one task have same period then RM randomly selects one for execution next [7]. c. DM Scheduling Algorithm DM Scheduling Algorithm is called Deadline Monotonic. DM also fixed or static priority Scheduling Algorithm. DM Scheduling Algorithm is depends on priority. In DM algorithm shortest priority gives first chances to execute but when more than one task have same priority then DM randomly selects one for execution next [2]. In DM Algorithm deadline is greater than execution time. DM is not give 100% result in under loaded situation. But DM gives better performance in overloaded situation as compare dynamic scheduling. d. EDF_RM Scheduling Algorithm EDF scheduling algorithm perform optimal in under loaded situation and RM scheduling algorithm perform better