Towards multiprogrammed GPUs

Programmable Graphics Processing Units (GPUs) have recently become the most pervasitheve massively parallel processors. They have come a long way, from fixed function ASICs designed to accelerate graphics tasks to a programmable architecture that can also execute general-purpose computations. Because of their performance and efficiency, an increasing amount of software is relying on them to accelerate data parallel and computationally intensive sections of code. They have earned a place in many systems, from low power mobile devices to the biggest data centers in the world. However, GPUs are still plagued by the fact that they essentially have no multiprogramming support, resulting in low system performance if the GPU is shared among multiple programs. In this dissertation we set to provide the rich GPU multiprogramming support by improving the multitasking capabilities and increasing the virtual memory functionality and performance. The main issue hindering the multitasking support in GPUs is the nonpreemptive execution of GPU kernels. Here we propose two preemption mechanisms with dierent design philosophies, that can be used by a scheduler to preempt execution on GPU cores and make room for some other process. We also argue for the spatial sharing of the GPU and propose a concrete hardware scheduler implementation that dynamically partitions the GPU cores among running kernels, according to their set priorities. Opposing the assumptions made in the related work, we demonstrate that preemptive execution is feasible and the desired approach to GPU multitasking. We further show improved system fairness and responsiveness with our scheduling policy. We also pinpoint that at the core of the insufficient virtual memory support lies the exceptions handling mechanism used by modern GPUs. Currently, GPUs offload the actual exception handling work to the CPU, while the faulting instruction is stalled in the GPU core. This stall-on-fault model prevents some of the virtual memory features and optimizations and is especially harmful in multiprogrammed environments because it prevents context switching the GPU unless all the in-flight faults are resolved. In this disseritation, we propose three GPU core organizations with varying performance-complexity trade-off that get rid of the stall-on-fault execution and enable preemptible exceptions on the GPU (i.e., the faulting instruction can be squashed and restarted later). Building on this support, we implement two use cases and demonstrate their utility. One is a scheme that performs context switch of the faulted threads and tries to find some other useful work to do in the meantime, hiding the latency of the fault and improving the system performance. The other enables the fault handling code to run locally, on the GPU, instead of relying on the CPU offloading and show that the local fault handling can also improve performance.Las Unidades de Procesamiento de Gráficos Programables (GPU, por sus siglas en inglés) se han convertido recientemente en los procesadores masivamente paralelos más difundidos. Han recorrido un largo camino desde ASICs de función fija diseñados para acelerar tareas gráficas, hasta una arquitectura programable que también puede ejecutar cálculos de propósito general. Debido a su rendimiento y eficiencia, una cantidad creciente de software se basa en ellas para acelerar las secciones de código computacionalmente intensivas que disponen de paralelismo de datos. Se han ganado un lugar en muchos sistemas, desde dispositivos móviles de baja potencia hasta los centros de datos más grandes del mundo. Sin embargo, las GPUs siguen plagadas por el hecho de que esencialmente no tienen soporte de multiprogramación, lo que resulta en un bajo rendimiento del sistema si la GPU se comparte entre múltiples programas. En esta disertación nos centramos en proporcionar soporte de multiprogramación para GPUs mediante la mejora de las capacidades de multitarea y del soporte de memoria virtual. El principal problema que dificulta el soporte multitarea en las GPUs es la ejecución no apropiativa de los núcleos de la GPU. Proponemos dos mecanismos de apropiación con diferentes filosofías de diseño, que pueden ser utilizados por un planificador para apropiarse de los núcleos de la GPU y asignarlos a otros procesos. También abogamos por la división espacial de la GPU y proponemos una implementación concreta de un planificador hardware que divide dinámicamente los núcleos de la GPU entre los kernels en ejecución, de acuerdo con sus prioridades establecidas. Oponiéndose a las suposiciones hechas por otros en trabajos relacionados, demostramos que la ejecución apropiativa es factible y el enfoque deseado para la multitarea en GPUs. Además, mostramos una mayor equidad y capacidad de respuesta del sistema con nuestra política de asignación de núcleos de la GPU. También señalamos que la causa principal del insuficiente soporte de la memoria virtual en las GPUs es el mecanismo de manejo de excepciones utilizado por las GPUs modernas. En la actualidad, las GPUs descargan el manejo de las excepciones a la CPU, mientras que la instrucción que causo la fallada se encuentra esperando en el núcleo de la GPU. Este modelo de bloqueo en fallada impide algunas de las funciones y optimizaciones de la memoria virtual y es especialmente perjudicial en entornos multiprogramados porque evita el cambio de contexto de la GPU a menos que se resuelvan todas las fallas pendientes. En esta disertación, proponemos tres implementaciones del pipeline de los núcleos de la GPU que ofrecen distintos balances de rendimiento-complejidad y permiten la apropiación del núcleo aunque haya excepciones pendientes (es decir, la instrucción que produjo la fallada puede ser reiniciada más tarde). Basándonos en esta nueva funcionalidad, implementamos dos casos de uso para demostrar su utilidad. El primero es un planificador que asigna el núcleo a otros subprocesos cuando hay una fallada para tratar de hacer trabajo útil mientras esta se resuelve, ocultando así la latencia de la fallada y mejorando el rendimiento del sistema. El segundo permite que el código de manejo de las falladas se ejecute localmente en la GPU, en lugar de descargar el manejo a la CPU, mostrando que el manejo local de falladas también puede mejorar el rendimiento.Postprint (published version

Biomechanical interactions between bone and metal-ceramic bridges composed of different types of non-noble alloys under vertical loading conditions

The purpose of this study was to compare the mechanical properties of three metal-ceramic bridges of different types of dental alloys and to present and evaluate the possible biomechanical interactions between a marginal bone and metal-ceramic bridges during vertical loading. The research was done as an experimental study. A mandible with an intact anterior region was used. The preparation of the remaining teeth for receiving three types of porcelain-fused-to-metal (PFM) restorations was performed. Vita VMK 95 was used for all three metal-ceramic restorations. These three metal-ceramic bridges composed of different alloys, nickel and non-nickel, served as different models: the Niadur-nickelferous model, the Wiron 99-nickel model and the Wirobond C-cobalt-chrome model. The maximum compressive strain of 5% for all three virtual models is observed in the region of central incisors. The Niadur model has the lowest mean strain (2.62%) in comparison with the other two models. The mean strain of Wiron 99 is lower, by 0.10%, than the mean strain of the Wirobond model. Biomechanical behavior of the presented models caused by the vertical-loading conditions is explained as an interaction between the marginal bone and the metal-ceramic bridges. All of them, nickel and non-nickel models, indicate a similar strain (deformation) distribution; however, from the biomechanical perspective, Niadur is more favorable than the other two materials

Analiza deformacija donje vilice optičkom metrologijom

Background/Aim. New optical stereometric methods based on both contact and noncontact mechanisms for displacement measurement have become common methods in biomechanical behavior research of biomaterials, bone and soft tissue. The aim of this study was to register and measure possible deformations of the lower jaw (mandible) with the intact dental arch using optical metrology method. Methods. The system for full field measurement of deformations (strains) comprised of two digital cameras for a synchronized stereoview of the specimen, and the Aramis software. Results. The maximum mandibular bone strains were measured in the regions of the lower first premolar and the lower second molar. In the action force of 500 N simulated in the region of the first lower premolar the intensity of deformation was 86 μm. The value of maximum strain in the bone around the molars was 24 μm for the force of 500 N acting on the second lower molar. When it comes to premolars, 3-5 times stronger deformation was observed in the region of the first lower premolar, compared to the deformation values of the second lower premolar area. Conclusion. Under loading of the applied forces the measured strains were in the elastic deformation area, meanning that the dependence of force and deformity is linear. The highest values of strain measurements obtained by the optical method were found in the jaw bone tissue around the loading teeth, and the bony regions of the triangle and mental region. According to the obtained results from the Aramis processing software it can be concluded that this method is applicable in a variety of biomedical research.Uvod/Cilj. Nove optičke stereometrijske metode koje se zasnivaju na kontaktnim i nekontaktnim mehanizmima za merenje zapremine postaju uobičajene metode u istraživanju biomehaničkog ponašanja biomaterijala, koštanog i mekog tkiva. Cilj ove studije bio je da se optičkom metodom merenja registruju i izmere eventualne deformacije koštanog fundamenta donje vilice sa intaktnim zubnim nizom i da se, ujedno, prikažu mogućnosti primene optičke metrologije u istraživanjima u stomatologiji. Metode. Sistem za merenje deformacija ispitivane donje vilice sa intaktnim zubnim lukom obuhvatio je dve digitalne kamere koje obezbeđuju stereosinhronizovani prikaz primerka, i softver Aramis. Rezultati. Najveće deformacije koštanog tkiva donje vilice izmerene su u regionu donjeg prvog premolara i donjeg drugog molara. Pri delovanju sila od 500 N za region prvog donjeg premolara veličina deformacije bila je 86 μm. Vrednost maksimalne srednje deformacije u koštanom sistemu oko molara iznosila je 24 μm pri delovanju sile od 500 N na drugi donji molar. Kada su u pitanju premolari, 3-5 puta jače deformacije uočene su u regionu prvog donjeg premolara, nego u predelu drugog donjeg premolara. Zaključak. Prilikom delovanja primenjenih sila deformacije se nalaze u elastičnom deformacionom polju, a međusobna zavisnost sile i deformacije ima linearan karakter. Najveće vrednosti deformacija dobijene optičkom metodom merenja registruju se u koštanom tkivu donje vilice koja je u neposrednom kontaktu sa zubima koji se opterećuju, kao i u koštanim regionima zakutnjačkog trougla i bradnog (mentalnog) otvora. Na osnovu analize rezultata dobijenih primenom softvera Aramis može se reći da postoje mogućnosti primene ove metode u različitim biomedicinskim istraživanjima

Eksperimentalna metodologija za određivanje uticaja dizajna dentalnih implanata na prenos opterećenja

Deformations in the vicinity of dental implants are affected by their design and if threshold level of 0.3 % is surpassed, bone resorption could occur. The goal of this study is to present a novel experimental approch for the analysis of effect od dental implant geometry on the surrounding structure strain values. A bone block model, with dimensions of 68x25x9 mm, was made from polymethyl-methacrylate. 3D printed block mold also provided a fixture for vertically placed Strauman ø4.0x12 mm. The sample was loaded in a three-point bending setup. The axial force of 600 N was applied on the dental implant. The Digital Image Correlation method was used for strain and displacement measurement. The highest von Mises strain of 0.7 % is located in the area of implant neck. The maximum displacement value in loading direction was 0.466 mm. Surface strain and displacement are correlated with implant geometry. This experimental methodology can be utilized to estimate dental implant load transfer characteristics.Dizajn dentalnih implanata utiče na vrednosti deformacija koje nastaju u njihovoj okolini, i ako se pređe granična vrednost od 0.3 %, može doći do resorpcije kosti. Cilj ove studije je da predstavi novi eksperimentalni pristup za analizu uticaja geometrije dentalnih implanata na deformacije okolne strukture. Model kosti, sa dimenzijama od 68h25h9 mm, je napravljen od polimetil-metakrilata. Kalup za model koji je napravljen pomoću tehnike 3D štampe, je takođe služio i kao fiksator položaja za vertikalno postavljeni implant Štrauman ø4.0x12 mm. Uzorak je opterećen na savijanje u tri tačke. Aksijalna sila od 600 N je primenjena na dentalni implant. Za merenje deformacija i pomeraja je korišćena metoda Digitalne korelacije slika. Najveće vrednosti Von Mizesovih deformacija od 0.7 % su izmerene u području vrata implanta. Maksimalne vrednosti pomeraja u pravcu opterećenja su iznosile 0.466 mm. Površinska deformacija i pomeraji su povezani sa geometrijom implanata. Ova eksperimentalna metodologija se može koristiti u cilju određivanja karakteristika prenosa opterećenja dentalnih

Strain field measurements of glass ionomer cement

Extensive evolution of glass ionomer cements (GIC) has marked a significant shift in the practice of luting indirect dental restorations limiting the use of zinc-phosphate and zinc-polycarboxylate cements to a few indications. GIC are now one of the materials of choice for cementation of all ceramics, fiber reinforced composite posts and veneers. GICs are determined by unique properties like chemical adhesion to tooth and base metals, low thermal expansion coefficients similar to dentin and minimal microleakage at the tooth-enamel interface due to low shrinkage. Shrinkage strain is identified as the cause, and the associated stress as the mechanism for the loss of marginal adaption and cohesive fracture within the material. The aim of this study is to measure the strain and displacement field in a conventional GIC (Riva Luting, SDI, Australia) related to different cement diameter, using 3D Digital Image Correlation (DIC) method. The experiment is done for samples with thickness of 1 mm combined with diameters of 4 mm (Group I) and 3 mm (Group II). The strain field is measured using 3D 11optical system Aramis 2M (GOM, Braunschweig, Germany). This study provides valuable data about strain behaviour and displacement as a possible failure factor in GIC, Riva Luting. Visible differences between Group I and Group II were observed

Strain field measurements of glass ionomer cement

Extensive evolution of glass ionomer cements (GIC) has marked a significant shift in the practice of luting indirect dental restorations limiting the use of zinc-phosphate and zinc-polycarboxylate cements to a few indications. GIC are now one of the materials of choice for cementation of all ceramics, fiber reinforced composite posts and veneers. GICs are determined by unique properties like chemical adhesion to tooth and base metals, low thermal expansion coefficients similar to dentin and minimal microleakage at the tooth-enamel interface due to low shrinkage. Shrinkage strain is identified as the cause, and the associated stress as the mechanism for the loss of marginal adaption and cohesive fracture within the material. The aim of this study is to measure the strain and displacement field in a conventional GIC (Riva Luting, SDI, Australia) related to different cement diameter, using 3D Digital Image Correlation (DIC) method. The experiment is done for samples with thickness of 1 mm combined with diameters of 4 mm (Group I) and 3 mm (Group II). The strain field is measured using 3D 11optical system Aramis 2M (GOM, Braunschweig, Germany). This study provides valuable data about strain behaviour and displacement as a possible failure factor in GIC, Riva Luting. Visible differences between Group I and Group II were observed

Experimental analysis of dental-implant load transfer in polymethyl-methacrylate blocks

Dental-implant overload can cause bone resorption. Load-transfer characteristics of dental implants are affected by their macro-design parameters. The goal of this study was to experimentally analyse the load-transfer characteristics of different dental implants, using polymethyl-methacrylate blocks. Three polymethyl-methacrylate blocks were created, with dimensions of (68 x 25 x 9) mm. Three dental implants, Nobel empty set3.5 mm x 15 mm, Strauman empty set4.1 mm x 10 mm and Strauman empty set4.8 mm x 12 mm. were placed in separate blocks. The samples were supported by a three-point-bending set-up and loaded with an axial force of 600 N. The 3D digital image correlation method was employed for strain and displacement measurements. The highest displacement and von Mises strain values were found for Strauman empty set4.1 mm x 10 mm (p lt 0.05), 0.186 mm and 0.596 %, respectively. The sample of Nobel empty set3.5 mm x 15 mm showed the lowest strain values. The sample of Strauman empty set4.8 mm x 12 mm (p > 0.05) had similar strain values as Nobel empty set3.5 mm x 15 mm. The load transfer during axial loading was primarily affected by the size of the implant contact surface. The displacement and strain values in the implant vicinity may provide an insight into the effect of dental-implant design on the load transfer

Izvori ispuštanja i zone opasnosti vodoničnih instalacija

У раду је дат преглед Српских прописа који дефинишу услове за безбедно држање, складиштење, транспорт и употребу водоника, као и преглед дефиниција зона опасности и сигурносних растојања око извора испуштања на водоничним инсталацијама који се уобичајено користе у нашој индустрији. У другом делу су дате зоне опасности дефинисане истим изворима испуштања израчунате према хармонизованом SRPS EN 60079-10-1:2017 и америчком NFPA 55:2020 стандарду. Наведени су и услови за држање водоника у лабораторијама, дефинисани NFPA 45:2020 стандардом.

Numerical Study of the Effect of Dental Implant Inclination

This paper contains the results of a research focused on the determination of the influence of an implant inclination on the strain state throughout the acrylic block with implant. The aim of the presented research is to qualitatively determine the regions with the greatest strain fields on the models. The finite element models of implant and acrylic block are developed for predefined implant inclinations in order to analyze the influence of implant inclination on deformations on the outer surface of acrylic block. The comparative contour plots of stress and strain state of analyzed models, as well as the comparative diagrams with obtained results, are presented. The conclusions about the inclination angle which leads to the higher strains in the block-implant are explained. Obtained results could be applied for the planning of future experimental studies which could utilize this and similar models to determine their load transfer characteristics, and could be included in the planning of dental implant position, and prediction of successful dental therapy

Experimental analysis of dental-implant load transfer in polymethyl-methacrylate blocks

Dental-implant overload can cause bone resorption. Load-transfer characteristics of dental implants are affected by their macro-design parameters. The goal of this study was to experimentally analyse the load-transfer characteristics of different dental implants, using polymethyl-methacrylate blocks. Three polymethyl-methacrylate blocks were created, with dimensions of (68 x 25 x 9) mm. Three dental implants, Nobel empty set3.5 mm x 15 mm, Strauman empty set4.1 mm x 10 mm and Strauman empty set4.8 mm x 12 mm. were placed in separate blocks. The samples were supported by a three-point-bending set-up and loaded with an axial force of 600 N. The 3D digital image correlation method was employed for strain and displacement measurements. The highest displacement and von Mises strain values were found for Strauman empty set4.1 mm x 10 mm (p lt 0.05), 0.186 mm and 0.596 %, respectively. The sample of Nobel empty set3.5 mm x 15 mm showed the lowest strain values. The sample of Strauman empty set4.8 mm x 12 mm (p > 0.05) had similar strain values as Nobel empty set3.5 mm x 15 mm. The load transfer during axial loading was primarily affected by the size of the implant contact surface. The displacement and strain values in the implant vicinity may provide an insight into the effect of dental-implant design on the load transfer