Real-Time Fixed and Dynamic Priority Driven Scheduling Algorithms: Theory and Experience

Projet REFLECSThere are two main positions regarding real-time scheduling algorithms. The first is based on fixed priorities and the second makes use of dynamic priorities such as deadlines. These two approaches have never really been compared because the emphasis has always been on the ease of implementation rather than the efficiency of the algorithms and the complexity of the associated feasibility conditions. In addition to traditional real-time applications, we believe that starting to look at these two criteria will be very important in the perspective of providing admission control mechanisms and real-time guarantees on large distributed systems like the Internet network. To that end, our purpose is first to provide a general framework based, on the one hand, a representation of preemptive, real-time scheduling in an algebraic structure that enables us to evaluate the distance of the optimality of any scheduling algorithm ; and on the other hand, a consistent representation of the associated feasibility conditions that enables us to evaluate the number of basic operations. As a second step, considering several kinds of traffics, we initiate the comparison by a straight, but limited, application of our general framework. Our preliminary results will notably highlight, in the cases where deadlines are all greater than periods, that fixed priority schedulers (like deadline monotonic) behave as well as EDF while the worst-case response time analysis is less complex. The same remark is valid when the task sets are almost homogeneous but is in favor of EDF in the general case or when a simple feasibility analysis is needed. Therefore, it might be of interest, given a real-time scheduling context (spanning from small embedded system to large distributed system), to take into account these two extra criteria in order to find a right trade-off among several possible solutions

Characterization of the Space of Feasible Worst-Case Execution Times for Earliest-Deadline-First scheduling

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A Norm Approach for the Partitioned EDF Scheduling of Sporadic Task Systems

International audienceIn this paper, we propose a new approach for the partitioned Earliest Deadline First (EDF) scheduling of sporadic task systems. We consider the case of constrained task deadlines where the deadlines of the tasks are less than or equal to their periods. We introduce the concept of the EDF norm, for defining the space of WCET values that result in schedulable systems given fixed periods and relative deadlines. Based on this concept, it is possible to derive a necessary and sufficient feasibility condition to check whether EDF scheduling is valid for a given partitioning. The EDF norm has interesting convexity properties that permit using a Linear Programming approach to reduce the number of points at which the EDF norm needs to be checked. From the EDF norm, we derive a New Worst Fit Decreasing partitioning heuristic and compare its performance with two existing partitioning heuristics based on density partitioning and demand bound function approximation. We then compare the performance of the heuristic in terms of the resource augmentation paradigm

Implementing reliable distributed real-time systems with the theta-model

Abstract. A widely accepted viewpoint is that designs for distributed real-time systems should be based on synchronous computational models. Safety in such designs, however, requires that the target system behaves as the synchronous model postulates. We believe that this approach is rather risky, as it rests on solving distributed scheduling problems which are known to be NP-hard. We therefore advocate the use of more relaxed system models, namely asynchronous models equipped with unreliable failure detectors. To this end, we introduce a novel implementation of the perfect failure detector, resting on an abstract model without upper bounds on end-toend message delays. Then, we demonstrate how this algorithm can be transferred from the abstract model intoarealnetwork/systemarchitecture. Finally, we prove that this solution exhibits real-time behavior.

Real-Time Fixed And Dynamic Priority Driven Scheduling Algorithms: Theory And Experience

There are two main positions regarding real-time scheduling algorithms. The first is based on fixed priorities and the second makes use of dynamic priorities such as deadlines. These two approaches have never really been compared because the emphasis has always been on the ease of implementation rather than the efficiency of the algorithms and the complexity of the associated feasibility conditions. In addition to traditional real-time applications, we believe that starting to look at these two criteria will be very important from the point of view of providing admission control mechanisms and real-time guarantees on large distributed systems like the Internet network. To that end, our purpose is first to provide a general framework based, on the one hand, a representation of preemptive, real-time scheduling in an algebraic structure that enables us to evaluate the distance of the optimality of any scheduling algorithm ; and on the other hand, a consistent representation of the assoc..

Mort volontaire combattante

Comment analyser ces pratiques suicidaires qui vont de l'immolation de soi sans victimes immédiates au geste kamikaze le plus meurtrier ? Que pouvons-nous comprendre aux motivations de leurs auteurs ? L'attentat-suicide serait-il devenu l'archétype même de l'acte brutal de violence qualifié de "terroriste" et le kamikaze, sa figure évidente ? A travers l'histoire et au-delà du Proche-Orient, ce numéro explore les logiques sacrificielles, les enjeux stratégiques de la mort volontaire combattante. Could the voluntary death of the combatant be a subject for research and reflection? How can one analyze the suicidal practices ranging from victimless self-immolation to the acts of the most murderous kamikaze? What do we understand of their authors’ motivations? Would suicidal-bombings have become the archetypal form of the violent acts we tend to describe  as « terrorism »? Would the kamikaze have become the obvious figure of such violence? Five years after 9/11, no one can ignore the role of passion when it comes to death, sacrifice and clandestine organisations resorting to devastating suicides as one of the possibilities within the array of conceivable actions.  This issue tries to open new research-perspectives while avoiding the common confusion between voluntary participation and fanaticism, between suicidal practices and ultimate self-sacrifice for a cause. Through history, and beyond the Middle East, this issue of Cultures & Conflict attempts exploring the logics of sacrifice and the strategic issues raised by voluntary death in combat. It also focuses on the reasons as well as on the social and individual conditions through which one could interpret this choice of death.

Rapamycin inhibits growth and survival of D816V-mutated c-kit mast cells.

International audienceTwo classes of oncogenic mutations of the c-kit tyrosine kinase have been described: the juxtamembrane domain V560G mutation, which is preferentially found in gastrointestinal stromal tumors (GISTs), and the kinase domain D816V mutation, which is highly representative of systemic mastocytosis (SM). Here we show that both mutations constitutively activate the mammalian target of rapamycin (mTOR) signaling pathway. Surprisingly, the mTOR inhibitor rapamycin induces only apoptosis in HMC-1 cells bearing the D816V but not the V560G mutation. In support of this unexpected selectivity, rapamycin inhibits the phosphorylation of 4E-BP1, a downstream substrate of the mTOR pathway, but only in D816V HMC-1 cells. Importantly, D816V mast cells isolated from SM patients or from transgenic mice are sensitive to rapamycin whereas normal human or mouse mast cells are not. Thus, rapamycin inhibition appears specific to the D816V mutation. At present there is no effective cure for SM patients with the D816V mutation. The data presented here provide a rationale to test whether rapamycin could be a possible treatment for SM and other hematologic malignancies with the D816V mutation