Real-time scheduling algorithms for multiprocessor systems have been the subject of considerable recent interest. For such an algorithm to be truly useful in practice, support for semaphore-based locking must be provided. However, for many global scheduling algorithms, no such mechanisms have been proposed. Furthermore, in the partitioned case, most prior semaphore schemes are either inefficient or restrict critical sections considerably. In this paper, a new flexible multiprocessor locking scheme is presented that can be applied under both partitioning and global scheduling. This scheme allows unrestricted critical-section nesting, but has been designed to deal with the common case of short non-nested accesses efficiently.
We consider the scheduling of a sporadic real-time task system on an identical multiprocessor. Though Pfair algorithms are theoretically optimal for such task systems, in practice, their runtime overheads can significantly reduce the amount of useful work that is accomplished. On the other hand, if all deadlines need to be met, then every known non-Pfair algorithm requires restrictions on total system utilization that can approach approximately 50% of the available processing capacity. This may be overkill for soft real-time systems, which can tolerate occasional or bounded deadline misses (i.e. bounded tardiness). In this paper we derive tardiness bounds under preemptive and non-preemptive global EDF when the total system utilization is not restricted, except that it not exceed the available processing capacity. Hence, processor utilization can be improved for soft real-time systems on multiprocessors. Our tardiness bounds depend on the total system utilization and per-task utilizations and execution costs-the lower these values, the lower the tardiness bounds. As a final remark, we note that global EDF may be superior to partitioned EDF for multiprocessorbased soft real-time systems in that the latter does not offer any scope to improve system utilization even if bounded tardiness can be tolerated.
When locking protocols are used in real-time systems, bounds on blocking times are required when ensuring timing constraints. While the term "blocking" is well-understood in the context of uniprocessor real-time systems, the same is not true in the multiprocessor case. In this paper, two definitions of blocking are presented that are applicable to suspensionbased multiprocessor locking protocols. The need for two definitions arises because of differences in how suspensions are handled in existing schedulability analysis. For each definition, locking protocols are presented that have asymptotically optimal blocking behavior. In particular, protocols are presented for any job-level static-priority global or partitioned scheduling algorithm.
In this paper, we consider variants of Pfair and ERfair scheduling in which subtasks may be released late, i.e., there may be separation between consecutive windows of the same task. We call such tasks intra-sporadic tasks. There are two main contributions of this paper. First, we show the existence of a Pfair (and hence ERfair) schedule for any intra-sporadic task system whose utilization is at most the number of available processors. Second, we give a polynomial-time algorithm that is optimal for scheduling intra-sporadic tasks in a Pfair or ERfair manner on systems of one or two processors.
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