Automatische Codegenerierung für Massiv Parallele Applikationen in der Numerischen Strömungsmechanik

Solving partial differential equations (PDEs) is a fundamental challenge in many application domains in industry and academia alike. With increasingly large problems, efficient and highly scalable implementations become more and more crucial. Today, facing this challenge is more difficult than ever due to the increasingly heterogeneous hardware landscape. One promising approach is developing domain‐specific languages (DSLs) for a set of applications. Using code generation techniques then allows targeting a range of hardware platforms while concurrently applying domain‐specific optimizations in an automated fashion. The present work aims to further the state of the art in this field. As domain, we choose PDE solvers and, in particular, those from the group of geometric multigrid methods. To avoid having a focus too broad, we restrict ourselves to methods working on structured and patch‐structured grids. We face the challenge of handling a domain as complex as ours, while providing different abstractions for diverse user groups, by splitting our external DSL ExaSlang into multiple layers, each specifying different aspects of the final application. Layer 1 is designed to resemble LaTeX and allows inputting continuous equations and functions. Their discretization is expressed on layer 2. It is complemented by algorithmic components which can be implemented in a Matlab‐like syntax on layer 3. All information provided to this point is summarized on layer 4, enriched with particulars about data structures and the employed parallelization. Additionally, we support automated progression between the different layers. All ExaSlang input is processed by our jointly developed Scala code generation framework to ultimately emit C++ code. We particularly focus on how to generate applications parallelized with, e.g., MPI and OpenMP that are able to run on workstations and large‐scale cluster alike. We showcase the applicability of our approach by implementing simple test problems, like Poisson’s equation, as well as relevant applications from the field of computational fluid dynamics (CFD). In particular, we implement scalable solvers for the Stokes, Navier‐Stokes and shallow water equations (SWE) discretized using finite differences (FD) and finite volumes (FV). For the case of Navier‐Stokes, we also extend our implementation towards non‐uniform grids, thereby enabling static mesh refinement, and advanced effects such as the simulated fluid being non‐Newtonian and non‐isothermal

System Designs for Diabetic Foot Ulcer Image Assessment

For individuals with type 2 diabetes, diabetic foot ulcers represent a significant health issue and the wound care cost is quite high. Currently, clinicians and nurses mainly base their wound assessment on visual examination of wound size and the status of the wound tissue. This method is potentially inaccurate for wound assessment and requires extra clinical workload. In view of the prevalence of smartphones with high resolution digital camera, assessing wound healing by analyzing of real-time images using the significant computational power of today’s mobile devices is an attractive approach for managing foot ulcers. Alternatively, the smartphone may be used just for image capture and wireless transfer to a PC or laptop for image processing. To achieve accurate foot ulcer image assessment, we have developed and tested a novel automatic wound image analysis system which accomplishes the following conditions: 1) design of an easy-to-use image capture system which makes the image capture process comfortable for the patient and provides well-controlled image capture conditions; 2) synthesis of efficient and accurate algorithms for real-time wound boundary determination to measure the wound area size; 3) development of a quantitative method to assess the wound healing status based on a foot ulcer image sequence for a given patient and 4) design of a wound image assessment and management system that can be used both in the patient’s home and clinical environment in a tele-medicine fashion. In our work, the wound image is captured by the camera on the smartphone while the patient’s foot is held in place by an image capture box, which is specially design to aid patients in photographing ulcers occurring on the sole of their feet. The experimental results prove that our image capture system guarantees consistent illumination and a fixed distance between the foot and camera. These properties greatly reduce the complexity of the subsequent wound recognition and assessment. The most significant contribution of our work is the development of five different wound boundary determination approaches based on different computer vision algorithms. The first approach employs the level set algorithm to determine the wound boundary directly based on a manually set initial curve. The second and third approaches are the mean-shift segmentation based methods augmented by foot outline detection and analysis. These two approaches have been shown to be efficient to implement (especially on smartphones), prior-knowledge independent and able to provide reasonably accurate wound segmentation results given a set of well-tuned parameters. However, this method suffers from the lack of self-adaptivity due to the fact that it is not based on machine learning. Consequently, a two-stage Support Vector Machine (SVM) binary classifier based wound recognition approach is developed and implemented. This approach consists of three major steps 1) unsupervised super-pixel segmentation, 2) feature descriptor extraction for each super-pixel and 3) supervised classifier based wound boundary determination. The experimental results show that this approach provides promising performance (sensitivity: 73.3%, specificity: 95.6%) when dealing with foot ulcer images captured with our image capture box. In the third approach, we further relax the image capture constraints and generalize the application of our wound recognition system by applying the conditional random field (CRF) based model to solve the wound boundary determination. The key modules in this approach are the TextonBoost based potential learning at different scales and efficient CRF model inference to find the optimal labeling. Finally, the standard K-means clustering algorithm is applied to the determined wound area for color based wound tissue classification. To train the models used in the last two approaches, as well as to evaluate all three methods, we have collected about 100 wound images at the wound clinic in UMass Medical School by tracking 15 patients for a 2-year period, following an IRB approved protocol. The wound recognition results were compared with the ground truth generated by combining clinical labeling from three experienced clinicians. Specificity and sensitivity based measures indicate that the CRF based approach is the most reliable method despite its implementation complexity and computational demands. In addition, sample images of Moulage wound simulations are also used to increase the evaluation flexibility. The advantages and disadvantages of three approaches are described. Another important contribution of this work has been development of a healing score based mechanism for quantitative wound healing status assessment. The wound size and color composition measurements were converted to a score number ranging from 0-10, which indicates the healing trend based on comparisons of subsequent images to an initial foot ulcer image. By comparing the result of the healing score algorithm to the healing scores determined by experienced clinicians, we assess the clinical validity of our healing score algorithm. The level of agreement of our healing score with the three assessing clinicians was quantified by using the Kripendorff’s Alpha Coefficient (KAC). Finally, a collaborative wound image management system between the PC and smartphone was designed and successfully applied in the wound clinic for patients’ wound tracking purpose. This system is proven to be applicable in clinical environment and capable of providing interactive foot ulcer care in a telemedicine fashion

Consideraciones acerca de la viabilidad de un sensor plenóptico en dispositivos de consumo

Doctorado en Ingeniería IndustrialPassive distance measurement of the objects in an image gives place to interesting applications that have the potential to revolutionize the field of photography. In this thesis a prototype of plenoptic camera for mobile devices was created and studied. This technique has two main disadvantages: the need for modifying the camera module and the loss of resolution. Because of this, the prototype was discarded in order to utilize another technique: depth from focus. In this technique the capture method consists in taking several images while varying the focus distance. The set of images is called focal-stack. Different focus operators are studied, which give a measure of defocus per pixel and plane of the focal-stack. The curvelet based focus operator is chosen as the most adequate. It is computationally more intensive than other operators but it is capable of decomposing natural images using few coefficients. In order to make viable its usage in mobile devices a new curvelet transform based on the discrete Radon transform is built. The discrete Radon transform has logarithmic complexity, does not use the Fourier transform and uses only integer sums. Lastly, different versions of the Radon transform are analyzed with the goal of achieving an even faster transform. These transforms are implemented to be executed on mobile devices. Additionally, an application of the Radon transform is presented. It consists in the detection of bar-codes that have any orientation in an image.La medida pasiva de distancia a los objetos en una imagen da lugar a interesantes aplicaciones con capacidad para revolucionar la fotografía. En esta tesis se creó y estudió un prototipo de cámara plenóptica para dispositivos móviles. Esta técnica presenta dos inconvenientes: la necesidad de modificar el módulo de cámara y la pérdida de resolución. Por ello, el prototipo fue descartado para utilizar otra técnica: la profundidad a partir del desenfoque. En esta técnica el método de captura consiste en tomar varias imagenes variando la distancia de enfoque. El conjunto de imágenes se denomina focal-stack. Se estudian distintos operadores de desenfoque, que dan una medida de desenfoque por pixel y por plano del focal-stack. Siendo elegido como óptimo el operador de desenfoque curvelet, que es computacionalmente más intensivo que otros operadores pero es capaz de descomponer imagenes naturales utilizando muy pocos coeficientes. Para hacer posible su uso en dispositivos móviles se construye una nueva transformada curvelet basada en la transformada discreta de Radon. La transformada discreta de Radon tiene complejidad linearítmica, no utiliza la transformada de Fourier y usa sólo sumas de enteros. Por último, se analizan distintas versiones de la transformada de Radon con el objetivo de conseguir una transformada aún más rápida y se implementan para ser ejecutadas en dispositivos móviles. Además se presenta una aplicación de la transformada de Radon consistente en la detección de códigos de barras con cualquier orientación en una imagen

Optimización del rendimiento y la eficiencia energética en sistemas masivamente paralelos

RESUMEN Los sistemas heterogéneos son cada vez más relevantes, debido a sus capacidades de rendimiento y eficiencia energética, estando presentes en todo tipo de plataformas de cómputo, desde dispositivos embebidos y servidores, hasta nodos HPC de grandes centros de datos. Su complejidad hace que sean habitualmente usados bajo el paradigma de tareas y el modelo de programación host-device. Esto penaliza fuertemente el aprovechamiento de los aceleradores y el consumo energético del sistema, además de dificultar la adaptación de las aplicaciones. La co-ejecución permite que todos los dispositivos cooperen para computar el mismo problema, consumiendo menos tiempo y energía. No obstante, los programadores deben encargarse de toda la gestión de los dispositivos, la distribución de la carga y la portabilidad del código entre sistemas, complicando notablemente su programación. Esta tesis ofrece contribuciones para mejorar el rendimiento y la eficiencia energética en estos sistemas masivamente paralelos. Se realizan propuestas que abordan objetivos generalmente contrapuestos: se mejora la usabilidad y la programabilidad, a la vez que se garantiza una mayor abstracción y extensibilidad del sistema, y al mismo tiempo se aumenta el rendimiento, la escalabilidad y la eficiencia energética. Para ello, se proponen dos motores de ejecución con enfoques completamente distintos. EngineCL, centrado en OpenCL y con una API de alto nivel, favorece la máxima compatibilidad entre todo tipo de dispositivos y proporciona un sistema modular extensible. Su versatilidad permite adaptarlo a entornos para los que no fue concebido, como aplicaciones con ejecuciones restringidas por tiempo o simuladores HPC de dinámica molecular, como el utilizado en un centro de investigación internacional. Considerando las tendencias industriales y enfatizando la aplicabilidad profesional, CoexecutorRuntime proporciona un sistema flexible centrado en C++/SYCL que dota de soporte a la co-ejecución a la tecnología oneAPI. Este runtime acerca a los programadores al dominio del problema, posibilitando la explotación de estrategias dinámicas adaptativas que mejoran la eficiencia en todo tipo de aplicaciones.ABSTRACT Heterogeneous systems are becoming increasingly relevant, due to their performance and energy efficiency capabilities, being present in all types of computing platforms, from embedded devices and servers to HPC nodes in large data centers. Their complexity implies that they are usually used under the task paradigm and the host-device programming model. This strongly penalizes accelerator utilization and system energy consumption, as well as making it difficult to adapt applications. Co-execution allows all devices to simultaneously compute the same problem, cooperating to consume less time and energy. However, programmers must handle all device management, workload distribution and code portability between systems, significantly complicating their programming. This thesis offers contributions to improve performance and energy efficiency in these massively parallel systems. The proposals address the following generally conflicting objectives: usability and programmability are improved, while ensuring enhanced system abstraction and extensibility, and at the same time performance, scalability and energy efficiency are increased. To achieve this, two runtime systems with completely different approaches are proposed. EngineCL, focused on OpenCL and with a high-level API, provides an extensible modular system and favors maximum compatibility between all types of devices. Its versatility allows it to be adapted to environments for which it was not originally designed, including applications with time-constrained executions or molecular dynamics HPC simulators, such as the one used in an international research center. Considering industrial trends and emphasizing professional applicability, CoexecutorRuntime provides a flexible C++/SYCL-based system that provides co-execution support for oneAPI technology. This runtime brings programmers closer to the problem domain, enabling the exploitation of dynamic adaptive strategies that improve efficiency in all types of applications.Funding: This PhD has been supported by the Spanish Ministry of Education (FPU16/03299 grant), the Spanish Science and Technology Commission under contracts TIN2016-76635-C2-2-R and PID2019-105660RB-C22. This work has also been partially supported by the Mont-Blanc 3: European Scalable and Power Efficient HPC Platform based on Low-Power Embedded Technology project (G.A. No. 671697) from the European Union’s Horizon 2020 Research and Innovation Programme (H2020 Programme). Some activities have also been funded by the Spanish Science and Technology Commission under contract TIN2016-81840-REDT (CAPAP-H6 network). The Integration II: Hybrid programming models of Chapter 4 has been partially performed under the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H2020 Programme. In particular, the author gratefully acknowledges the support of the SPMT Department of the High Performance Computing Center Stuttgart (HLRS)

Programming models for mobile environments

Premi extraordinari doctorat UPC curs 2017-2018. Àmbit d’Enginyeria de les TICFor the last decade, mobile devices have grown in popularity and became the best-selling computing devices. Despite their high capabilities for user interactions and network connectivity, the computing power of mobile devices is low and the lifetime of the application running on them limited by the battery. Mobile Cloud Computing (MCC) is a technology that tackles the limitations of mobile devices by bringing together their mobility with the vast computing power of the Cloud. Programming applications for Mobile Cloud Computing (MCC) environments is not as straightforward as coding monolithic applications. Developers have to deal with the issues related to parallel programming for distributed infrastructures while considering the battery lifetime and the variability of the network produced by the high mobility of this kind of devices. As with any other distributed environment, developers turn to programming models to improve their productivity by avoiding the complexity of manually dealing with these issues and delegate on the corresponding model all the management of these concerns. This thesis contributes to the current state of the art with an adaptation of the COMPSs programming model for MCC environments. COMPSs allows application programmers to code their applications in a sequential, infrastructure-agnostic fashion without calls to any COMPSs-specific API using the native language for the target platform as if they were to run on the mobile device. At execution time, a runtime system automatically partitions the application into tasks and orchestrates their execution on top of the available resources. This thesis contributes with an extension to the programming model to allow task polymorphism and let the runtime exploit computational resources other than the CPU of the resources. Besides, the runtime architecture has been redesigned with the characteristics of MCC in mind, and it runs as a common service which all the applications running simultaneously on the mobile device contact for submitting the execution of their tasks. For collaboratively exploiting both, local and remote resources, the runtime clusters the computational devices into Computing Platforms according to the mechanisms required to provide the processing elements with the necessary input values, launch the task execution avoiding resource oversubscription and fetching the results back from them. The CPU Platform run tasks on the cores of the CPU. The GPU Platform leverages on OpenCL to run tasks as kernels on GPUs or other accelerators embedded in the mobile device. Finally, the Cloud Platform offloads the execution of tasks onto remote resources. To holistically decide whether is worth running a task on embedded or on remote resources, the runtime considers the the costs -- time, energy and money -- of running the computation on each of the platforms and picks the best. Each platform manages internally its resources and orchestrates the execution of tasks on them using different scheduling policies. Using local and remote computing devices forces the runtime to share data values among the nodes of the infrastructure. This data is potentially privacy-sensitive, and the runtime exposes it to possible attackers when transferring it through the network. To protect the application user from data leaks, the runtime has to provide communications with secrecy, integrity and authenticity. In the extreme case of a network breakdown that isolates the mobile device from the remote nodes, the runtime has to ensure that the execution continues to provide the application user with the expected result even if the connection never re-establishes. The mobile device has to respond using only the resources embedded in it, what could incur in the re-execution of computations already ran on the remote resources. Remote workers have to continue with the execution so that, in case of reconnection, both parts synchronize its progress to reduce the impact of the disruption.Els últims anys, els dispositius mòbils han guanyat en popularitat i s'han convertit en els dispositius més venuts. Tot i la connectivitat i la bona interacció amb l'usuari que ofereixen, la seva capacitat de càlcul is baixa i limitada per la vida de la bateria. El Mobile Cloud Computing (MCC) és una tecnologia que soluciona les limitacions d'aquests dispositius ajuntant la seva mobilitat amb la gran capacitat de còmput del Cloud. Programar aplicacions per entorns MCC no és tan directe com fer aplicacions monolítiques. Els desenvolupadors han de tractar amb els problemes relacionats amb la programació paral·lela mentre tenen en compte la duració de la bateria i la variabilitat de la xarxa degut a la mobilitat inherent a aquest tipus de dispositius. Com per qualsevol altre entorn distribuït, els desenvolupadors recorren a models de programació que millorin la seva productivitat i els evitin tractar manualment amb aquests problemes delegant la seva gestió en el model. Aquesta tesis contribueix a l'estat de l'art actual amb una adaptació del model de programació COMPSs als entorns MCC. COMPSs permet als desenvolupadors programar les aplicacions de forma agnòstica a la infraestructura i seqüencial sense necessitat d'invocar cap API específica utilitzant el llenguatge natiu de la platforma com si l'aplicació s'executés directament en el mòbil. En temps d'execució, una eina (runtime) automàticament divideix l'aplicació en tasques i n'orquestra la seva execució sobre els recursos disponibles. Aquesta tesis estèn el model de programació per tal de permetre polimorfisme a nivell de tasca i deixar al runtime explotar els recursos computacionals dels que disposa el mòbil a part de la CPU. A més a més, l'arquitectura del runtime s'ha redissenyat tenint en compte les característiques pròpies del MCC, i aquest s'executa com un servei comú al que totes les aplicacions del mòbil contacten per tal d'executar les seves tasques. Per explotar col·laborativament tots els recursos, locals i remots, el runtime agrupa els recursos en Computing Platforms en funció dels mecanismes necessaris per proveir el recurs amb les dades d'entrada necessàries, llançar l'execució i recuperar-ne els resultats. La CPU Platform executa tasques en els nuclis de la CPU. La GPU Platform utilitza OpenCL per executar tasques en forma de kernels a la GPU o altres acceleradors integrats en el mòbil. Finalment, la Cloud Platform descàrrega l'execució de tasques en recursos remots. Per decidir holisticament si és millor executar una tasca en un recurs local o en un remot, el runtime considera els costs (temporal, energètic econòmic) d'executar la tasca en cada una de les plataformes i n'escull la millor. Cada plataforma gestiona internament els seus recursos i orquestra l'execució de les tasques en ells seguint diferents polítiques de planificació. L'ús de recursos locals i remots força la compartició de dades entre els nodes de la infraestructura. Aquestes dades són potencialment sensibles i de caràcter privat i el runtime les exposa a possibles atacs que les transfereix per la xarxa. Per tal de protegir l'usuari de possibles fuites de dades, el runtime ha de dotar les comunicacions amb confidencialitat, integritat i autenticitat. En el cas extrem en que un error de xarxa aïlli el dispositiu mòbil dels nodes remots, el runtime ha d'assegurar que l'execució continua i que eventualment l'usuari rebrà el resultat esperat fins i tot en cas de que la connexió no és restableixi mai. El mòbil ha de ser capaç d'executar l'aplicació utilitzant únicament les dades i recursos disponibles en aquell moment, la qual cosa pot forçar la re-execució d'algunes tasques ja calculades en els recursos remots. Els recursos remots han de continuar l'execució per tal que en cas de reconnexió, ambdues parts sincronitzin el seu progrés i es minimitzi l'impacte de la desconnexió.Award-winningPostprint (published version

Programming models for mobile environments

For the last decade, mobile devices have grown in popularity and became the best-selling computing devices. Despite their high capabilities for user interactions and network connectivity, the computing power of mobile devices is low and the lifetime of the application running on them limited by the battery. Mobile Cloud Computing (MCC) is a technology that tackles the limitations of mobile devices by bringing together their mobility with the vast computing power of the Cloud. Programming applications for Mobile Cloud Computing (MCC) environments is not as straightforward as coding monolithic applications. Developers have to deal with the issues related to parallel programming for distributed infrastructures while considering the battery lifetime and the variability of the network produced by the high mobility of this kind of devices. As with any other distributed environment, developers turn to programming models to improve their productivity by avoiding the complexity of manually dealing with these issues and delegate on the corresponding model all the management of these concerns. This thesis contributes to the current state of the art with an adaptation of the COMPSs programming model for MCC environments. COMPSs allows application programmers to code their applications in a sequential, infrastructure-agnostic fashion without calls to any COMPSs-specific API using the native language for the target platform as if they were to run on the mobile device. At execution time, a runtime system automatically partitions the application into tasks and orchestrates their execution on top of the available resources. This thesis contributes with an extension to the programming model to allow task polymorphism and let the runtime exploit computational resources other than the CPU of the resources. Besides, the runtime architecture has been redesigned with the characteristics of MCC in mind, and it runs as a common service which all the applications running simultaneously on the mobile device contact for submitting the execution of their tasks. For collaboratively exploiting both, local and remote resources, the runtime clusters the computational devices into Computing Platforms according to the mechanisms required to provide the processing elements with the necessary input values, launch the task execution avoiding resource oversubscription and fetching the results back from them. The CPU Platform run tasks on the cores of the CPU. The GPU Platform leverages on OpenCL to run tasks as kernels on GPUs or other accelerators embedded in the mobile device. Finally, the Cloud Platform offloads the execution of tasks onto remote resources. To holistically decide whether is worth running a task on embedded or on remote resources, the runtime considers the the costs -- time, energy and money -- of running the computation on each of the platforms and picks the best. Each platform manages internally its resources and orchestrates the execution of tasks on them using different scheduling policies. Using local and remote computing devices forces the runtime to share data values among the nodes of the infrastructure. This data is potentially privacy-sensitive, and the runtime exposes it to possible attackers when transferring it through the network. To protect the application user from data leaks, the runtime has to provide communications with secrecy, integrity and authenticity. In the extreme case of a network breakdown that isolates the mobile device from the remote nodes, the runtime has to ensure that the execution continues to provide the application user with the expected result even if the connection never re-establishes. The mobile device has to respond using only the resources embedded in it, what could incur in the re-execution of computations already ran on the remote resources. Remote workers have to continue with the execution so that, in case of reconnection, both parts synchronize its progress to reduce the impact of the disruption.Els últims anys, els dispositius mòbils han guanyat en popularitat i s'han convertit en els dispositius més venuts. Tot i la connectivitat i la bona interacció amb l'usuari que ofereixen, la seva capacitat de càlcul is baixa i limitada per la vida de la bateria. El Mobile Cloud Computing (MCC) és una tecnologia que soluciona les limitacions d'aquests dispositius ajuntant la seva mobilitat amb la gran capacitat de còmput del Cloud. Programar aplicacions per entorns MCC no és tan directe com fer aplicacions monolítiques. Els desenvolupadors han de tractar amb els problemes relacionats amb la programació paral·lela mentre tenen en compte la duració de la bateria i la variabilitat de la xarxa degut a la mobilitat inherent a aquest tipus de dispositius. Com per qualsevol altre entorn distribuït, els desenvolupadors recorren a models de programació que millorin la seva productivitat i els evitin tractar manualment amb aquests problemes delegant la seva gestió en el model. Aquesta tesis contribueix a l'estat de l'art actual amb una adaptació del model de programació COMPSs als entorns MCC. COMPSs permet als desenvolupadors programar les aplicacions de forma agnòstica a la infraestructura i seqüencial sense necessitat d'invocar cap API específica utilitzant el llenguatge natiu de la platforma com si l'aplicació s'executés directament en el mòbil. En temps d'execució, una eina (runtime) automàticament divideix l'aplicació en tasques i n'orquestra la seva execució sobre els recursos disponibles. Aquesta tesis estèn el model de programació per tal de permetre polimorfisme a nivell de tasca i deixar al runtime explotar els recursos computacionals dels que disposa el mòbil a part de la CPU. A més a més, l'arquitectura del runtime s'ha redissenyat tenint en compte les característiques pròpies del MCC, i aquest s'executa com un servei comú al que totes les aplicacions del mòbil contacten per tal d'executar les seves tasques. Per explotar col·laborativament tots els recursos, locals i remots, el runtime agrupa els recursos en Computing Platforms en funció dels mecanismes necessaris per proveir el recurs amb les dades d'entrada necessàries, llançar l'execució i recuperar-ne els resultats. La CPU Platform executa tasques en els nuclis de la CPU. La GPU Platform utilitza OpenCL per executar tasques en forma de kernels a la GPU o altres acceleradors integrats en el mòbil. Finalment, la Cloud Platform descàrrega l'execució de tasques en recursos remots. Per decidir holisticament si és millor executar una tasca en un recurs local o en un remot, el runtime considera els costs (temporal, energètic econòmic) d'executar la tasca en cada una de les plataformes i n'escull la millor. Cada plataforma gestiona internament els seus recursos i orquestra l'execució de les tasques en ells seguint diferents polítiques de planificació. L'ús de recursos locals i remots força la compartició de dades entre els nodes de la infraestructura. Aquestes dades són potencialment sensibles i de caràcter privat i el runtime les exposa a possibles atacs que les transfereix per la xarxa. Per tal de protegir l'usuari de possibles fuites de dades, el runtime ha de dotar les comunicacions amb confidencialitat, integritat i autenticitat. En el cas extrem en que un error de xarxa aïlli el dispositiu mòbil dels nodes remots, el runtime ha d'assegurar que l'execució continua i que eventualment l'usuari rebrà el resultat esperat fins i tot en cas de que la connexió no és restableixi mai. El mòbil ha de ser capaç d'executar l'aplicació utilitzant únicament les dades i recursos disponibles en aquell moment, la qual cosa pot forçar la re-execució d'algunes tasques ja calculades en els recursos remots. Els recursos remots han de continuar l'execució per tal que en cas de reconnexió, ambdues parts sincronitzin el seu progrés i es minimitzi l'impacte de la desconnexió

Finding, Measuring, and Reducing Inefficiencies in Contemporary Computer Systems

Computer systems have become increasingly diverse and specialized in recent years. This complexity supports a wide range of new computing uses and users, but is not without cost: it has become difficult to maintain the efficiency of contemporary general purpose computing systems. Computing inefficiencies, which include nonoptimal runtimes, excessive energy use, and limits to scalability, are a serious problem that can result in an inability to apply computing to solve the world's most important problems. Beyond the complexity and vast diversity of modern computing platforms and applications, a number of factors make improving general purpose efficiency challenging, including the requirement that multiple levels of the computer system stack be examined, that legacy hardware devices and software may stand in the way of achieving efficiency, and the need to balance efficiency with reusability, programmability, security, and other goals. This dissertation presents five case studies, each demonstrating different ways in which the measurement of emerging systems can provide actionable advice to help keep general purpose computing efficient. The first of the five case studies is Parallel Block Vectors, a new profiling method for understanding parallel programs with a fine-grained, code-centric perspective aids in both future hardware design and in optimizing software to map better to existing hardware. Second is a project that defines a new way of measuring application interference on a datacenter's worth of chip-multiprocessors, leading to improved scheduling where applications can more effectively utilize available hardware resources. Next is a project that uses the GT-Pin tool to define a method for accelerating the simulation of GPGPUs, ultimately allowing for the development of future hardware with fewer inefficiencies. The fourth project is an experimental energy survey that compares and combines the latest energy efficiency solutions at different levels of the stack to properly evaluate the state of the art and to find paths forward for future energy efficiency research. The final project presented is NRG-Loops, a language extension that allows programs to measure and intelligently adapt their own power and energy use