Scheduling Approaches for Large-Scale Complex Task Management Hashem Ali Ghazzawi Real-Time Systems Group, Department of Computer Science, The University of York, UK hag@cs.york.ac.uk Abstract The emergence of complex real-time systems (RTS) can be widely witnessed in industry. We have organisational job handling across heterogeneous, largely independent and/or interdependent environments with high computing tasks to be shared across large areas/countries. We need techniques to assure scheduling tasks efficiently and meeting their deadlines within an acceptable range, overall stability, efficient monitoring and maintainability. Traditional real-time computing assumes worst-case requirements are known a priori. This will provide guarantees in avoid- ance of undesirable effects such as overload and deadline misses. In LSCITS, one of the main concerns is to design adaptation capabilities that handle uncer- tain effects dynamically and in an analytically predictable manner. Classical real- time scheduling algorithms such as EDF and RM are considered to be open loop techniques. Meaning that the end result is not fed back to the system to improve the performance (minimise the error). The benefit of feeding back and comput- ing the system error is that we would agree on what actions to take to achieve the desired behaviour to acceptable range. Here, actions are either increasing the CPU/memory/network utilisations or assigning different priorities to tasks etc. In other words, these algorithms work appropriately in predicted environments where tasks execution times and deadlines are known a priori. This is not the case with LSCITS, the need of being able to monitor the system performance and constantly having knowledge of the errors margin is highly desired. Control theory offers feedback system modelling where it makes working in such an LSCITS environ- ment is manageable and delivers acceptable results. Modelling a computing system as a dynamic system or as a controller is an approach that has proved to be fruitful in many cases. Keywords: Real-time systems, Scheduling algorithms, Feedback control 1 The State of Today’s IT Systems The drama of “IT systems keep on failing” is witnessed in our society more often these days e.g. the failure of the Heathrow Terminal 5 in March 2008. It has been always the case that the failure of IT systems occupies the front news headlines, but not the successful ones though. Thus, there is the demand for solving the issues, why fail, of 1