S-adic characterization of minimal ternary dendric shifts

Dendric shifts are defined by combinatorial restrictions of the extensions of the words in their languages. This family generalizes well-known families of shifts such as Sturmian shifts, Arnoux-Rauzy shifts and codings of interval exchange transformations. It is known that any minimal dendric shift has a primitive S-adic representation where the morphisms in S are positive tame automorphisms of the free group generated by the alphabet. In this paper we investigate those S-adic representations, heading towards an S-adic characterization of this family. We obtain such a characterization in the ternary case, involving a directed graph with 2 vertices

Towards QoS-Oriented SLA Guarantees for Online Cloud Services

International audienceCloud Computing provides a convenient means of remote on-demand and pay-per-use access to computing resources. However, its ad hoc management of quality-of-service and SLA poses significant challenges to the performance, dependability and costs of online cloud services. The paper precisely addresses this issue and makes a threefold contribution. First, it introduces a new cloud model, the SLAaaS (SLA aware Service) model. SLAaaS enables a systematic integration of QoS levels and SLA into the cloud. It is orthogonal to other cloud models such as SaaS or PaaS, and may apply to any of them. Second, the paper introduces CSLA, a novel language to describe QoS-oriented SLA associated with cloud services. Third, the paper presents a control-theoretic approach to provide performance, dependability and cost guarantees for online cloud services, with time-varying workloads. The proposed approach is validated through case studies and extensive experiments with online services hosted in clouds such as Amazon EC2. The case studies illustrate SLA guarantees for various services such as a MapReduce service, a cluster-based multi-tier e-commerce service, and a low-level locking service

Un algorithme équitable d'exclusion mutuelle distribuée avec priorité

National audienceLes algorithmes distribués d'exclusion mutuelle à priorité permettent de définir un ordre d'accès aux sections critiques protégeant des ressources partagées. Ces algorithmes sont très utiles dans les applications temps-réel ou pour assurer différents niveaux de qualité de service [6]. Cependant, la prise en compte des priorités peut conduire à des famines dans le cas où des demandes de sections critique les plus prioritaires empêchent la satisfaction des moins prioritaires. Pour palier ce problème, certains algorithmes comme celui de Kanrar-Chaki proposent d'incrémenter progressivement les priorités des requêtes pendantes mais ceci peut conduire à une violation de l'ordre des priorités. Ainsi, pour minimiser ces violations sans engendrer de famine et de surplus de messages, nous proposons des modifications de l'algorithme de Kanrar-Chaki pour ralentir la fréquence d'incrémentation des priorités. Nos évaluations des performances confirment l'efficacité de notre approche

A fair starvation-free prioritized mutual exclusion algorithm for distributed systems

International audienceSeveral distributed mutual exclusion algorithms define the order in which requests are satisfied based on the priorities assigned to requests. These algorithms are very useful for real-time applications ones or those where priority is associated to a quality of service requirement. However, priority based strategies may result in starvation problems where high priority requests forever prevent low priority ones to be satisfied. To overcome this problem, many priority-based algorithms propose to gradually increase the priority of pending requests. The drawback of such an approach is that it can violate priority-based order of requests leading to priority inversion. Therefore, aiming at minimizing the number of priority violations without introducing starvation, we have added some heuristics in Kanrar-Chaki priority-based token-oriented algorithm in order to slow down the frequency with which priority of pending requests is increased. Performance evaluation results confirm the effectiveness of our approach when compared to both the original Kanrar-Chaki and Chang's priority-based algorithms

Highlighting the Container Memory Consolidation Problems in Linux

International audienceThe container mechanism supports server consolidation ; to ensure memory performance isolation, Linux relies on static memory limits. However, this results in poor performance, because an application needs are dynamic. In this article we will show current problems with memory consolidation for containers in Linux

Towards multi-SDN services: Dangers of concurrent resource allocation from multiple providers

International audienceOne of the Software-Defined Networking (SDN) promises is the programmability of networks through Application Programming Interfaces (APIs). Those APIs allow different users to access the network concurrently. Thus leading to the allocation of dedicated critical resources by a given Service Provider. In this paper we formalize the problem of deadlocks , and present a case where they occur

MemOpLight: Leveraging application feedback to improve container memory consolidation

International audienceThe container mechanism amortizes costs by consolidating several servers onto the same machine, while keeping them mutually isolated.Specifically, to ensure performance isolation, Linux relies on memory limits.These limits are static, despite the fact that application needs are dynamic; this results in poor performance.To solve this issue, MemOpLight uses dynamic application feedback to rebalance physical memory allocation between containers focusing on under-performing ones.This paper presents the issues, explains the design of MemOpLight, and validates it experimentally.Our approach increases total satisfaction by 13% compared to the default

Age Effects on Upper Limb Kinematics Assessed by the REAplan Robotin Healthy School-Aged Children

The use of kinematics is recommended to quantitatively evaluate upper limb movements. The aims of this study were to determine the age effects on upper limb kinematics and establish norms in healthy children. Ninetythree healthy children, aged 3–12 years, participated in this study. Twenty-eight kinematic indices were computed from four tasks. Each task was performed with the REAplan, a distal effector robotic device that allows upper limb displacements in the horizontal plane. Twenty-four of the 28 indices showed an improvement during childhood. Indeed, older children showed better upper limb movements. This study was the first to use a robotic device to show the age effects on upper limb kinematics and establish norms in healthy children