249 research outputs found
Une grille d'Ă©valuation pour les analyseurs syntaxiques
International audienceLes techniques d'Ă©valuation aujourd'hui disponibles posent un certain nombre de problĂšmes Ă la fois pour ce qui concerne la disponibilitĂ© des ressources nĂ©cessaires, mais Ă©galement dans la mesure oĂč elles ne reflĂštent pas complĂštement des vĂ©ritables capacitĂ©s d'un systĂšme. Nous proposons dans cet article l'Ă©laboration d'une grille d'analyse qui constitue une description standardisĂ©e des caractĂ©ristiques du systĂšme. Cette grille contient Ă la fois des aspects purement descriptifs (concernant par exemple le formalisme ou les aspects algorithmiques) ainsi qu'un ensemble de mesures automatisĂ©es, le tout donnant une image plus prĂ©cise du systĂšme qu'une simple Ă©valuation quantitative
Kerrighed: A SSI Cluster OS Running OpenMP
Writing parallel programs for clusters of workstations is still a challenging task. In this paper, we present Kerrighed, a Single System Image (SSI) operating system giving the illusion of an SMP machine, and providing the standard posix thread interface to developers. It is therefore possible to use Kerrighed to run OpenMP programs compiled for SMP-machines using the posix thread interface. In this paper, we explain how we managed to achieve that goal, and present the benefits of providing OpenMP support through the SSI approach as opposed to a dedicated run-time environment
Ghost Process: a Sound Basis to Implement Process Duplication, Migration and Checkpoint/Restart in Linux Clusters
Process management mechanisms (process duplication, migration and checkpoint/restart) are very useful for high performance and high availability in clustering systems. The single system image approach aims at providing a global process management service with mechanisms for process checkpoint, process migration and process duplication. In this context, a common mechanism for process virtualization is highly desirable but traditional operating systems do not provide such a mecahnism. This paper presents a kernel service for process virtualization called ghost process, extending the Linux kernel. The ghost process mechanism has been implemented in the Kerrighed single system image based on Linux. \\ Les mécanismes de gestion de processus (duplication, migration et création de point de reprise/reprise de processus) sont particuliÚrement intéressants pour les systÚmes pour grappes de calculateurs à haute performance et à haute disponibilité. L'un des buts des systÚmes à image unique est d'offrir un service de gestion globale des processus fondé sur des mécamismes de création de points de reprise de processus, de migration de processus et de duplication de processus. Dans ce contexte, un mécanisme commun pour la virtualisation de processus est hautement bénéfique mais les systÚmes d'exploitation traditionnels n'offrent pas un tel mécanisme. Ce document présente un service noyau pour la virtualisation de processus, appelé processus fantÎme, fondé sur une extension du noyau Linux. Le mécanisme de processus fantÎme a été mis en oeuvre dans le systÚme à image unique Kerrughed fondé sur Linux
Electroactivity of phototrophic river biofilms and constitutive cultivable bacteria
Electroactivity is a property of microorganisms assembled in biofilms that has been highlighted in a variety of environments. This characteristic was assessed for phototrophic river biofilms at the community scale and at the bacterial population scale. At the community scale, electroactivity was evaluated on stainless steel and copper alloy coupons used both as biofilm colonization supports and as working electrodes. At the population scale, the ability of environmental bacterial strains to catalyze oxygen reduction was assessed by cyclic voltammetry. Our data demonstrate that phototrophic river biofilm development on the electrodes, measured by dry mass and chlorophyll a content, resulted in significant increases of the recorded potentials, with potentials of up to +120 mV/saturated calomel electrode (SCE) on stainless steel electrodes and +60 mV/SCE on copper electrodes. Thirty-two bacterial strains isolated from natural phototrophic river biofilms were tested by cyclic voltammetry. Twenty-five were able to catalyze oxygen reduction, with shifts of potential ranging from 0.06 to 0.23 V, cathodic peak potentials ranging from â0.36 to â0.76 V/SCE, and peak amplitudes ranging from â9.5 to â19.4 ÎŒA. These isolates were diversified phylogenetically (Actinobacteria, Firmicutes, Bacteroidetes, and Alpha-, Beta-, and Gammaproteobacteria) and exhibited various phenotypic properties (Gram stain, oxidase, and catalase characteristics). These data suggest that phototrophic river biofilm communities and/or most of their constitutive bacterial populations present the ability to promote electronic exchange with a metallic electrode, supporting the following possibilities: (i) development of electrochemistry-based sensors allowing in situ phototrophic river biofilm detection and (ii) production of microbial fuel cell inocula under oligotrophic conditions
Ensemble Learning for Efficient VVC Bitrate Ladder Prediction
Changing the encoding parameters, in particular the video resolution, is a
common practice before transcoding. To this end, streaming and broadcast
platforms benefit from so-called bitrate ladders to determine the optimal
resolution for given bitrates. However, the task of determining the bitrate
ladder can usually be challenging as, on one hand, so-called fit-for-all static
ladders would waste bandwidth, and on the other hand, fully specialized ladders
are often not affordable in terms of computational complexity. In this paper,
we propose an ML-based scheme for predicting the bitrate ladder based on the
content of the video. The baseline of our solution predicts the bitrate ladder
using two constituent methods, which require no encoding passes. To further
enhance the performance of the constituent methods, we integrate a conditional
ensemble method to aggregate their decisions, with a negligibly limited number
of encoding passes. The experiment, carried out on the optimized software
encoder implementation of the VVC standard, called VVenC, shows significant
performance improvement. When compared to static bitrate ladder, the proposed
method can offer about 13% bitrate reduction in terms of BD-BR with a
negligible additional computational overhead. Conversely, when compared to the
fully specialized bitrate ladder method, the proposed method can offer about
86% to 92% complexity reduction, at cost the of only 0.8% to 0.9% coding
efficiency drop in terms of BD-BR
A New Approach to Configurable Dynamic Scheduling in Clusters based on Single System Image Technologies
Clusters are now considered as an alternative to parallel machines to execute workloads made up of sequential and/or parallel applications. For efficient application execution on clusters, dynamic global process scheduling is of prime importance. Different dynamic scheduling policies that have been studied for distributed systems or parallel machines may be used in clusters. The choice of a particular policy depends on the kind of workload to be executed. In a cluster, it is thus highly desirable to implement a configurable global scheduler to be able to adapt the dynamic scheduling policy to the workload characteristics, to take benefit of all cluster resources and tocope with node shutdown and reboot. In this paper, we present the architecture of the global scheduler and the process management mechanisms of Kerrighed, a single system image operating system designed for high performance computing on clusters. Kerrighed provides a development framework allowing to easily implement dynamic scheduling policies without kernel modification. In Kerrighed, the global scheduling policy can be dynamically changed while applications execute on the cluster. Kerrighed's process management mechanisms allow to easily deploy parallelapplications in the cluster and to efficiently migrate or checkpoint processes, including processes sharing memory. Kerrighed has been implemented as a set of modules extending Linux kernel. Preliminary performance results are presented
Embedding OLTC nonlinearities in predictive Volt Var Control for active distribution networks
Volatile productions and consumptions generate a stochastic behavior of distribution grids and make its supervision difficult to achieve. Usually, the Distributed Generators reactive powers are adjusted to perform decentralized voltage control. Industrial controllers are generally equipped with a local affine feedback law, which settings are tuned at early stage using local data. A centralized and more efficient tuning method should aim to maximize the probability that all the node voltages of distribution grids remain within prescribed bounds. When the characteristics of the stochastic power forecasts are known, the centralized algorithm allows to update the settings on a regular time basis. However, the method requires to solve stochastic optimization problem. Assuming that stochastic variables have Gaussian distributions, a procedure is given which guarantees the convergence of the stochastic optimization. Convex problems drastically reduce the difficulty and the computational time required to reach the global minimum, compared to nonconvex optimal power flow problems. The linear controllers with optimized parameters are compared to traditional control laws using simulations of a real distribution grid model. The results show that the algorithm is reliable and moreover fast enough. Hence, the proposed method can be used to update periodically the control parameters
- âŠ