Faithful Performance Prediction of a Dynamic Task-Based Runtime System for Heterogeneous Multi-Core Architectures

International audienceSUMMARY Multi-core architectures comprising several GPUs have become mainstream in the field of High-Performance Computing. However, obtaining the maximum performance of such heterogeneous machines is challenging as it requires to carefully offload computations and manage data movements between the different processing units. The most promising and successful approaches so far build on task-based runtimes that abstract the machine and rely on opportunistic scheduling algorithms. As a consequence, the problem gets shifted to choosing the task granularity, task graph structure, and optimizing the scheduling strategies. Trying different combinations of these different alternatives is also itself a challenge. Indeed, getting accurate measurements requires reserving the target system for the whole duration of experiments. Furthermore, observations are limited to the few available systems at hand and may be difficult to generalize. In this article, we show how we crafted a coarse-grain hybrid simulation/emulation of StarPU, a dynamic runtime for hybrid architectures, over SimGrid, a versatile simulator of distributed systems. This approach allows to obtain performance predictions of classical dense linear algebra kernels accurate within a few percents and in a matter of seconds, which allows both runtime and application designers to quickly decide which optimization to enable or whether it is worth investing in higher-end GPUs or not. Additionally, it allows to conduct robust and extensive scheduling studies in a controlled environment whose characteristics are very close to real platforms while having reproducible behavior

Faithful Performance Prediction of a Dynamic Task-based Runtime System, an Opportunity for Task Graph Scheduling

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Modeling Irregular Kernels of Task-based codes: Illustration with the Fast Multipole Method

The significant increase of the hardware complexity that occurred in the last few years led the high performance community to design many scientific libraries according to a task-based parallelization. The modeling of the performance of the individual tasks (or kernels) they are composed of is crucial for facing multiple challenges as diverse as performing accurate performance predictions, designing robust scheduling algorithms, tuning the applications, etc. Fine-grain modeling such as emulation and cycle-accurate simulation may lead to very accurate results. However, not only their high cost may be prohibitive but they furthermore require a high fidelity modeling of the processor, which makes them hard to deploy in practice. In this paper, we propose an alternative coarse-grain, empirical methodology oblivious to both the target code and the hardware architecture, which leads to robust and accurate timing predictions. We illustrate our approach with a task-based Fast Multipole Method (FMM) algorithm, whose kernels are highly irregular, implemented in the \scalfmm library on top of the starpu task-based runtime system and the simgrid simulator.L'augmentation significative de la complexité matérielle qui s'est produite ces quelques dernières années a amené la communauté de calcul haute performance à mettre au point de nombreuses bibliothèques scientifiques sur le principe d'une parallélisation à base de tâches. La modélisation de la performance des tâches individuelles (ou noyaux) qui les composent est cruciale pour faire face aux multiples challenges aussi variés que la réalisation de prédictions de performance précises, la mise au point d'algorithme d'ordonnancement robustes, l'optimisation des applications, etc. La modélisation à grain fin tel que l'émulation et la simulation à la précision du cycle peut permettre des résultats très précis. Toutefois, non seulement leur coût élevé peut être prohibitif mais elles requièrent de surcroît une modélisation très fidèle du processeur, ce qui les rend difficiles à déployer en pratique. Dans ce papier, nous proposons une méthodologie alternative, à plus gros grain, empirique, transparente à la fois pour le code et l'architecture cibles, ce qui permet des prédictions robustes et précises. Nous illustrons notre approche avec une méthode méthode multipolaire rapide (FMM) à base de tâches, dont les noyaux sont hautement irréguliers, implémentée dans la librairie ScalFMM au-dessus du moteur d'exécution StarPU et du simulateur SimGrid

Evaluation of quality of TB control services by private health care providers in Plateau state, Nigeria; 2012

Introduction: Tuberculosis (TB) is public health concern in Nigeria. The country uses the Directly  Observed Treatment Short course (DOTS) strategy for its control. Plateau state started using the DOTS strategy in 2001 and had the Private health facilities (PHF) as an important stakeholder. We evaluated their contributions to case finding and quality of the services to identify gaps in monitoring and evaluation in the TB control services within the PHF to plan for intervention so as to meet the set target for TB control in the state. Methods: We used the logical framework approach to identify and analyze the  problem. We drew up an objective tree and from the objective tree developed a logical framework matrix including evaluation plan. We also conducted desk review to extract data on case findings, case  management and outcomes of the treatment. We interviewed TB focal persons and laboratory personnel using structured questionnaire. The data was analyzed using excel spread sheet. Results: Of the 127 health facilities with TB patients on treatment 27 (21.3%) were PHF. The PHF reported 54.6% (1494) of TB cases in 2011. The sputum conversion rates, cured rate, treatment success rate, and default rates were 85%, 73%, 81.4% and 6.6% respectively. The discordant rates were 3.1% and 1.2% for the state and private health facilities respectively. Conclusion: Log frame approach is a useful tool for evaluation of TB control services and helps provide evidence for decision making to improve quality of the TB services in the public and private health facilities in the state.Key words: Private facilities, Tuberculosis, monitoring and evaluation, Logframe approac

Modeling and Simulation of a Dynamic Task-Based Runtime System for Heterogeneous Multi-Core Architectures

International audienceMulti-core architectures comprising several GPUs have become mainstream in the field of High-Performance Computing. However, obtaining the maximum performance of such heterogeneous machines is challenging as it requires to carefully offload computations and manage data movements between the different processing units. The most promising and successful approaches so far rely on task-based runtimes that abstract the machine and rely on opportunistic scheduling algorithms. As a consequence, the problem gets shifted to choosing the task granularity, task graph structure, and optimizing the scheduling strategies. Trying different combinations of these different alternatives is also itself a challenge. Indeed, getting accurate measurements requires reserving the target system for the whole duration of experiments. Furthermore, observations are limited to the few available systems at hand and may be difficult to generalize. In this article, we show how we crafted a coarse-grain hybrid simulation/emulation of StarPU, a dynamic runtime for hybrid architectures, over SimGrid, a versatile simulator for distributed systems. This approach allows to obtain performance predictions accurate within a few percents on classical dense linear algebra kernels in a matter of seconds, which allows both runtime and application designers to quickly decide which optimization to enable or whether it is worth investing in higher-end GPUs or not

O-Doped Nanographenes: A Pyrano/Pyrylium Route Towards Semiconducting Cationic Mixed-Valence Complexes

Herein we report an efficient synthesis to prepare O-doped nanographenes derived from the π-extension of pyrene. The derivatives are highly fluorescent and feature low oxidation potentials. Using electrooxidation, crystals of cationic mixed-valence (MV) complexes were grown in which the organic salts organize into face-to-face π-stacks, a favorable solid-state arrangement for organic electronics. Variable-temperature electron paramagnetic resonance (EPR) measurements and relaxation studies suggest a strong electron delocalization along the longitudinal axis of the columnar π-stacking architectures. Electric measurements of single crystals of the MV salts show a semiconducting behavior with a remarkably high conductivity at room temperature. These findings support the notion that π-extension of heteroatom-doped polycyclic aromatic hydrocarbons is an attractive approach to fabricate nanographenes with a broad spectrum of semiconducting properties and high charge mobilities

Detecção de Anomalias de Desempenho em Aplicações de Alto Desempenho baseadas em Tarefas em Clusters Híbridos

National audienceProgramming paradigms in High-Performance Computing have been shifting towards task-based models which are capable to more readily adapt to heterogeneous and scalable supercomputers. Detecting performance anomalies in such environments is particularly difficult since it must consider architecture heterogeneity, variability, and the capability to obtain trusted measurements. This work presents a case-study about the detection of anomalies in the execution of the well-known tiled dense Cholesky factorization developed with StarPU. Our experiments have been conducted in a variety of hybrid multi-node platforms to demonstrate how we are capable to detect and highlight performance anomalies.Os paradigmas de programação em Computação de Alto Desempe-nho estão mudando para modelos baseados em tarefas que são capazes de se adaptar a supercomputadores com arquiteturas heterogêneas e escaláveis. A detecção de anomalias de desempenho em tal cenário é particularmente difícil uma vez que ela deve considerar a heterogeneidade da arquitetura, a variabili-dade e a capacidade de obter medições confiáveis. Este trabalho apresenta um estudo de caso sobre a detecção de anomalias na execução da conhecida fatora-ção de Cholesky por blocos desenvolvida com StarPU. Os experimentos foram conduzidos em uma variedade de plataformas com múltiplos nós híbridos para demonstrar a capacidade de detectar e destacar anomalias de desempenho

Factors associated with interruption of treatment among Pulmonary Tuberculosis patients in Plateau State, Nigeria. 2011

Introduction: Nigeria has one of the highest tuberculosis (TB) burdens in the world with estimated  incidence of 133 per 100,000 populations. Multi-drug resistant TB (MDR-TB) is an emerging threat of the  TB control in Nigeria caused mainly by incomplete treatment. This study explored factors that affect  adherence to treatment among patients undergoing direct observation of TB treatment in Plateau state,  Nigeria.Methods: Between June and July 2011, we reviewed medical records and interviewed randomly selected pulmonary TB patients in their eighth month of treatment. Information on patients? clinical, socio- demographic and behavioral characteristics was collected using checklist and structured questionnaire for knowledge of treatment duration and reasons for interruption of treatment. We conducted focus group discussions with patients about barriers to treatment adherence. Data were analyzed with Epi Info  software. Results: Of 378 records reviewed, 229 (61%) patients were male; mean age 37.6 ±13.5 years and 71 (19%) interrupted their treatment. Interruption of treatment was associated with living > 5 km from TB treatment site (AOR: 11.3; CI 95%: 5.7-22.2), lack of knowledge of duration of treatment (AOR: 6.1; CI 95%: 2.8-13.2) and cigarette smoking (AOR: 3.4; CI 95%: 1.5- 8.0). Major reasons for the interruption were lack of transport fare (40%) and feeling well (25%). Focused group discussions revealed unfriendly attitudes of health care workers as barriers to adherence to treatment. Conclusion: This study revealed knowledge of the patients on the duration of treatment, distance and health workers  attitude as the major determinants of adherent to TB treatment. Training for health care workers on  patient education was conducted during routine supportive supervision.Key words: Interruption, treatment, Tuberculosis, Nigeri

Design of a debris removal & on-orbit maintenance mission for mega-constellations

This paper shows the results of the design of a mission providing a service of maintenance and removal of mega-constellations. The innovative concept inspiring the design of DeBROOM 2 , Debris Removal and On-Orbit Maintenance Mission, is that a combination of different services can be performed in a modular and standardized way by a single unit servicing satellites in each orbital plane of the constellation. This is achieved through a servicer, which carries both the equipment to refuel target satellites and active-debris removal and propulsive kits, dedicated to the extension of the mission lifetime of cooperative OneWeb satellites, via the takeover of the attitude and orbital control system, as well as to de-orbit uncooperative faulty OneWeb satellites from LEO. The design covers all the areas of system level design, including the definition of system and mission requirements, concept of operations, and mission concept design, along with the design of the servicer and propulsive kits. The paper highlights and identifies the key challenges, the main drivers, and the major traded-off options during the mission concept design. Particular focus is given to the mission analysis aspects, with a computation of the delta-V that characterizes the key maneuvers necessary to serve one or a selection of orbital planes constituting the mega-constellation. The feasibility of the mission is demonstrated by the relevant budgets, along with the utilization of high TRL and COTS components in almost all the key elements of the mission