The scheduling of sporadic task systems upon multiprocessor platforms is considered, when inter-processor migration is permitted. It is known that current schedulability tests for such systems perform quite poorly when compared to schedulability tests for partitioned scheduling. Limitations of current tests are identified, which may be responsible for the unsatisfactory performance of these tests. A new test that overcomes some of these limitations is proposed and proved correct. Current state

more »

... f the art. Currently, the partitioned scheduling of sporadic task systems is much better understood than global scheduling. Sufficient schedulability tests of polynomial time-complexity have been designed [7, 17, 8] for various commonly-used scheduling algorithms (such as Earliest Deadline First (EDF) [22, 14] and Deadline Monotonic (DM) [21] ). Worst-case resourceaugmentation bounds, that provide a quantitative measure of how effective these tests are, have been obtained. These schedulability tests have also been extensively evaluated via simulations [4, 6] , and shown to have much better averagecase behavior than indicated by their worst-case guarantees. In contrast, we are not aware of non-trivial theoretical bounds on the performance of known sufficient schedulability tests [2, 3, 10] for global scheduling (other than a relatively naive resource-augmentation bound on global DM [16]), and simulation experiments have tended to indicate that they perform poorly in comparison to the partitioned schedulability tests. This research. This research is aimed at obtaining a better understanding of global schedulability for sporadic task systems. After formally defining the task and machine models in Section 2, we start out in Section 3 by highlighting what appears to be one of the root causes of difficulty in such analysis: our failure thus far to come up with tech-