PetaQCD : En Route for the automatic code generation for lattice QCD

International audienceNew computer architectures with various weak and strong characteristics appear with increasing speed. We present our work in progress for the tool-chain aimed at rapid prototyping of the novel dirac matrix inversion algorithms for emerging architectures. From scientific description of the algorithm on the front end to the several back ends we discuss how symbolic manipulation may be used to create and optimize lattice calculations on the fly

Simulation study of driver stress and performance to an unexpected event

Abstract In this paper, we study the effect of unexpected behaviour of a Driving Assistance System (DAS) on the driver, during a common task of driving in a virtual environment. The considered system is an electrical steering, which allows drivers to reduce efforts needed to handle the steering wheel during cornering manoeuvres. A failure of such system could produce a sudden and permanent loss of steering assistance and make the steering wheel more difficult to turn. The objective of this study is to determine how this event will affect the driver's performance, particularly in terms of stress and visual performance. At last, drivers are able to adapt to this kind of event if it occurs before entering a curve. Moreover, an increase of muscle stiffness has been observed during lane change manoeuvres, which provide a more robust control of the steering wheel to external perturbations. At last drivers are able to manage a sudden increase of stress. The experiment was conducted on the ULTIMATE dynamic driving simulator developed by the Technical Centre for Simulation of RENAULT. The simulator has been fitted with a new steering force feedback system improving dynamical performance. This simulator upgrade and assessment methodology will be presented in more details in this paper. The driver behaviour was studied through questionnaires to assess the stress produced by the different situations. Detection and/or recognition of objects in the virtual scene give cues on the DAS failure effects on the driver's visual attention. In order to quantify the drivers' performance, objective indicators such as steering reversal rate, steering entropy and time-to-lane-crossing were also used. In spite of the unexpected steering event, all drivers have achieved their driving task, without leaving the road. Results show an increase of stress for drivers when the unexpected event occurs. We also notice an alteration of the visual performance revealed by drivers' difficulties to recognize critical objects in the environment. This study suggests that high-performance driving simulators may be valuable to assess the effects of safety-critical events on driving performance. Résumé Dans cet article, nous étudions l'effet sur le conducteur d'un comportement inattendu d'un système d'aide à la conduite (DAS) et ceci lors d'une tâche de conduite ordinaire en environnement virtuel. Le système retenu est une direction assistée électrique qui permet au conducteur de réduire les efforts nécessaires à produire pour le maniement du volant en virage. Une défaillance d'un tel système peut produire une perte soudaine et permanente d'assistance et rendre ainsi le volant plus difficile à tourner. L'objectif de cette étude est de déterminer l'impact de ce type d'évènement sur les performances du conducteur. Seront considérés en particulier la performance visuelle et la production de stress. Il a été constaté que lorsque cet évènement apparaît avant l'entrée en virage, les conducteurs sont capables de s'y adapter. De plus, une augmentation de la raideur des muscles du bras a été observée lors de manoeuvres de changement de file, ce qui rend le contrôle du volant plus robuste à des perturbations extérieures. Enfin, il semble que les conducteurs sont capables de gérer un stress soudain et de courte durée. L'expérimentation a été réalisée sur le simulateur de conduite dynamique ULTIMATE développé au Centre Technique de Simulation de RENAULT. Le simulateur s'est vu doté d'un nouveau restituteur d'effort pour le volant, offrant des performances dynamiques supérieures au précédent restituteur. L'installation et la validation de ce nouveau matériel sera présentée dans de plus amples détails. Le comportement des conducteurs a été étudié au travers de questionnaires afin d'évaluer la production de stress lors des différentes situations. La détection et/ou la reconnaissance d'objets dans la scène virtuelle procure des indices quant aux effets sur l'attention visuelle du conducteur de la défaillance du système d'assistance. Dans le but de quantifier la performance de conduite, des indicateurs tels que le Steering Reversal Rate, le Steering Entropy et le Time-to-Line-Crossing ont été utilisés. Malgré que l'évènement soit inattendu, tous les conducteurs ont réussi à terminer leur tâche de conduite sans quitter la route. Les résultats montrent une augmentation du stress lorsque cet évènement apparaît. Remarquons aussi l'altération de l'attention visuelle des conducteurs de part leur difficulté à reconnaître les objets de l'environnement. Cette étude suggère que les simulateurs de conduite à hautes performances autorisent l'évaluation des effets sur la performance de conduite d'évènements critiques en termes de sécurité

Rewriting System for Profile-Guided Data Layout Transformations on Binaries

International audienceCareful data layout design is crucial for achieving high performance. However exploring data layouts is time-consuming and error-prone, and assessing the impact of a layout transformation on performance is difficult without performing it. We propose to guide application programmers through data layout restructuring by providing a comprehensive multidimensional description of the initial layout, built from trace analysis, and then by giving a performance evaluation of the transformations tested and an expression of each transformed layout. The programmer can limit the exploration to layouts matching some patterns. We apply this method to two multithreaded applications. The performance prediction of multiple transformations matches within 5% the performance of hand-transformed layout code

From Driving Simulation to Virtual Reality

Driving simulation from the very beginning of the advent of VR technology uses the very same technology for visualization and similar technology for head movement tracking and high end 3D vision. They also share the same or similar difficulties in rendering movements of the observer in the virtual environments. The visual-vestibular conflict, due to the discrepancies perceived by the human visual and vestibular systems, induce the so-called simulation sickness, when driving or displacing using a control device (ex. Joystick). Another cause for simulation sickness is the transport delay, the delay between the action and the corresponding rendering cues. Another similarity between driving simulation and VR is need for correct scale 1:1 perception. Correct perception of speed and acceleration in driving simulation is crucial for automotive experiments for Advances Driver Aid System (ADAS) as vehicle behavior has to be simulated correctly and anywhere where the correct mental workload is an issue as real immersion and driver attention is depending on it. Correct perception of distances and object size is crucial using HMDs or CAVEs, especially as their use is frequently involving digital mockup validation for design, architecture or interior and exterior lighting. Today, the advents of high resolution 4K digital display technology allows near eye resolution stereoscopic 3D walls and integrate them in high performance CAVEs. High performance CAVEs now can be used for vehicle ergonomics, styling, interior lighting and perceived quality. The first CAVE in France, built in 2001 at Arts et Metiers ParisTech, is a 4 sided CAVE with a modifiable geometry with now traditional display technology. The latest one is Renault’s 70M 3D pixel 5 sides CAVE with 4K x 4K walls and floor and with a cluster of 20 PCs. Another equipment recently designed at Renault is the motion based CARDS driving simulator with CAVE like 4 sides display system providing full 3D immersion for the driver. The separation between driving simulation and digital mockup design review is now fading though different uses will require different simulation configurations. New application domains, such as automotive AR design, will bring combined features of VR and driving simulation technics, including CAVE like display system equipped driving simulators

An Effective Automated Approach to Specialization of Code

Abstract. Application performance is heavily dependent on the compiler optimizations. Modern compilers rely largely on the information made available to them at the time of compilation. In this regard, specializing the code according to input values is an effective way to communicate necessary information to the compiler. However, the static specialization suffers from possible code explosion and dynamic specialization requires runtime compilation activities that may degrade the overall performance of the application. This article proposes an automated approach for specializing code that is able to address both the problems of code size increase and the overhead of runtime activities. We first obtain optimized code through specialization performed at static compile time and then generate a template that can work for a large set of values through runtime specialization. Our experiments show significant improvement for different SPEC benchmarks on Itanium-II(IA-64) and Pentium-IV processors using icc and gcc compilers.

Iterative Compilation with Kernel Exploration

Abstract. The increasing complexity of hardware mechanisms for recent processors makes high performance code generation very challenging. One of the main issue for high performance is the optimization of memory accesses. General purpose compilers, with no knowledge of the application context and approximate memory model, seem inappropriate for this task. Combining applicationdependent optimizations on the source code and exploration of optimization parameters as it is achieved with ATLAS, has been shown as one way to improve performance. Yet, hand-tuned codes such as in the MKL library still outperform ATLAS with an important speed-up and some effort has to be done in order to bridge the gap between performance obtained by automatic and manual optimizations. In this paper, a new iterative compilation approach for the generation of high performance codes is proposed. This approach is not application-dependent, compared to ATLAS. The idea is to separate the memory optimization phase from the computation optimization phase. The first step automatically finds all possible decompositions of the code into kernels. With datasets that fit into the cache and simplified memory accesses, these kernels are simpler to optimize, either with the compiler, at source level, or with a dedicated code generator. The best decomposition is then found by a model-guided approach, performing on the source code the required memory optimizations. Exploration of optimization sequences and their parameters is achieved with a meta-compilation language, X language. The first results on linear algebra codes for Itanium show that the performance obtained reduce the gap with those of highly optimized hand-tuned codes.