Pau Mendoza UPVLC pabmench@disca.upv.es Patricia Balbastre UPVLC patricia@disca.upv.es Alfons Crespo UPVLC alfons@disca.upv.es 2003 OCERA Consortium \n \n \n \n \n EDF scheduler for RTLinux Scheduling, Real-Time, Aperiodic, QoS CBS scheduling policy efficiently handle soft real-time requests with a variable or unknown execution behaviour under EDF scheduling policy. This component modifies the RTLinux source code to support this scheduling policy. The Constant Bandwidth Server (CBS) [Abeni98] was developed to efficiently handle soft real-time requests with a variable or unknown execution behaviour under EDF scheduling policy. To avoid unpredictable delays on hard real-time tasks, soft tasks are solated through a bandwidth reservation mechanism, according to wich each soft task s assigned a fraction of the CPU and it is scheduled in such a way that it will never demand more than its reserved bandwidth, independently of its actual requests. This is achieved by assigning each soft task a deadline, computed as a function of the reserved bandwidth and its actual requests. If a task requires to execute more than its expected computation time, its deadline is postponed so that its reserved bandwidth is not exceeded. As a consequence, overruns ocurring on a served task will only delay that task, without compromising the bandwidth assigned to other tasks. By isolating the effects of task overloads, hard tasks can be guaranteed using classical schedulability analysis.