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LRETL: An optimal multiprocessor algorithm for sporadic task sets
 in International Conference on RealTime and Network Systems (RTNS
, 2009
"... This article presents a detailed discussion of LRETL (Local Remaining Execution TLplane), an algorithm that schedules hard realtime periodic and sporadic task sets with unconstrained deadlines on identical multiprocessors. The algorithm builds upon important concepts such as the TLplane constru ..."
Abstract

Cited by 8 (1 self)
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This article presents a detailed discussion of LRETL (Local Remaining Execution TLplane), an algorithm that schedules hard realtime periodic and sporadic task sets with unconstrained deadlines on identical multiprocessors. The algorithm builds upon important concepts such as the TLplane construct used in the development of the LLREF algorithm (Largest Local Remaining Execution First). This article identifies of the fundamental TLplane scheduling principles used in the construction of LLREF. These simple principles are examined, identifying methods of simplifying the algorithm and allowing it to handle a more general task model. For example, we identify the principle that total local utilization can never increase within any TLplane as long as a minimal number of tasks are executing. This observation leads to a straightforward approach for scheduling task arrivals within a TLplane. In this manner LRETL can schedule sporadic tasks and tasks with unconstrained deadlines. Like LLREF, the LRETL scheduling algorithm is optimal for task sets with implicit deadlines. In addition, LRETL can schedule task sets with unconstrained deadlines provided they satisfy the density test for multiprocessor systems. While LLREF has a O(n 2) runtime per TLplane, LRETL’s runtime is O(n log n) per TLplane. 1.
Improved Conditions for Bounded Tardiness under EPDF Pfair Multiprocessor Scheduling ✩
"... The earliestpseudodeadlinefirst (EPDF) Pfair algorithm is more efficient than other known Pfair scheduling algorithms, but is not optimal for scheduling recurrent realtime task systems on more than two identical processors. Although not optimal, EPDF may be preferable for realtime systems insta ..."
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The earliestpseudodeadlinefirst (EPDF) Pfair algorithm is more efficient than other known Pfair scheduling algorithms, but is not optimal for scheduling recurrent realtime task systems on more than two identical processors. Although not optimal, EPDF may be preferable for realtime systems instantiated on lesspowerful platforms, those with soft timing constraints, or those whose task composition can change at runtime. In prior work, Srinivasan and Anderson established a sufficient pertask utilization restriction for ensuring a tardiness of at most q quanta, where q ≥ 1, under EPDF. They also conjectured that under this algorithm, a tardiness bound of one quantum applies to task systems that are not subject to any restriction other than the obvious restrictions, namely, that the total system utilization not exceed the available processing capacity and pertask utilizations not exceed 1.0. In this paper, we present counterexamples that show that their conjecture is false and present sufficient pertask utilization restrictions that are more liberal than theirs. For ensuring a tardiness bound of one quantum, our restriction presents an improvement of 50 % over the previous one. Key words: soft realtime, multiprocessors, Pfairness, scheduling, tardiness bounds