http://hdl.handle.net/2117/3126 2013-05-22T09:22:05Z http://hdl.handle.net/2117/19366 Title: IT or not to be: the impact of Moodle in the education of developing countries Authors: García Almiñana, Jordi; Somé, Michel; Ayguadé Parra, Eduard; Cabré Garcia, José M.; Casany Guerrero, María José; Frigola Bourlon, Manel; Galanis, Nikolaos; García-Cervigon Gutiérrez, Manuel; Guerrero Zapata, Manel; Muñoz Gracia, María del Pilar Abstract: E-learning environments, such as Moodle, provide a technology that fosters the improvement of the educational system in developed countries, where education is traditionally performed with relatively high standards of quality. A large number of case studies and research have been conducted to demonstrate how e-learning technologies can be applied to improve both training and learning processes. However, these technologies have not been proved efficient when applied to developing countries. The challenges that must be addressed in developing countries, both technological and societal, are much more complex and the possible solution margins are more constrained than those existing in the context where these technologies have been created. In this paper we show how Moodle can be used to improve the quality of education in developing countries and, even more important, how can be used to turn the educational system more sustainable and effective in the long-term. We describe our experience in implementing a programming course in Moodle for the Higher School of Informatics at the Université Polytechnique de Bobo-Dioulasso, in Burkina Faso (West Africa), joining efforts with local professors in designing and implementing the learning system. The case example has been designed having in mind a number of contextual problems: lack of lecturers, excessive teaching hours per lecturer, massive classes, and curricula organization and stability, among others. We finally discuss how the teaching effort is reduced, the students’ knowledge and capacity improves, and the institutional academic model can be guaranteed with the proposal. For this reason, we claim that information technologies in developing countries are a cost-effective way to guarantee the objectives originally defined in the academic curricula and, therefore, deal with the problem of the education. 2013-05-22T07:16:25Z http://hdl.handle.net/2117/19282 Title: Supporting stateful tasks in a dataflow graph Authors: Gajinov, Vladimir; Stipic, Srdjan; Unsal, Osman Sabri; Harris, Tim; Ayguadé Parra, Eduard; Cristal Kestelman, Adrián Abstract: This paper introduces Atomic Dataflow Model (ADF) - a programming model for shared-memory systems that combines aspects of dataflow programming with the use of explicitly mutable state. The model provides language constructs that allow a programmer to delineate a program into a set of tasks and to explicitly define input data for each task. This information is conveyed to the ADF runtime system which constructs the task dependency graph and builds the necessary infrastructure for dataflow execution. However, the key aspect of the proposed model is that it does not require the programmer to specify all of the task’s dependencies exp licitly, but only those that imply logical ordering between tasks. The ADF model manages the remainder of inter-task dependencies automatically, by executing the body of the task within an implicit memory transaction. This provides an easy- to -program optimistic concurrency substrate and enables a task to safely share data with other concurrent tasks. In this paper, we describe the ADF model and show how it can increase the programmability of shared memory systems. 2013-05-16T10:26:49Z http://hdl.handle.net/2117/19279 Title: Transactional access to shared memory in StarSs, a task based programming model Authors: Gayatri, Rahulkumar; Badia Sala, Rosa Maria; Ayguadé Parra, Eduard; Lujan, M; Watson, I. Abstract: With an increase in the number of processors on a single chip, programming environments which facilitate the exploitation of par- allelism on multicore architectures have become a necessity. StarSs is a task-based programming model that enables a flexible and high level programming. Although task synchronization in StarSs is based on data flow and dependency analysis, some applications (e.g. reductions )require locks to access shared data. Transactional Memory is an alternative to lock-based synchronization for controlling access to shared data. In this paper we explore the idea of integrating a lightweight Software Transactional Memory (STM) library, TinySTM , into an implementation of StarSs (SMPSs). The SMPSs run- time and the compiler have been modified to include and use calls to the STM library. We evaluated this approach on four applications and observe better performance in applications with high lock contention. 2013-05-16T09:52:14Z http://hdl.handle.net/2117/19276 Title: Vector extensions for decision support DBMS acceleration Authors: Hayes, Timothy; Palomar Pérez, Óscar; Unsal, Osman Sabri; Cristal Kestelman, Adrián; Valero Cortés, Mateo Abstract: Database management systems (DBMS) have become an essential tool for industry and research and are often a significant component of data centres. As a result of this criticality, efficient execution of DBMS engines has become an important area of investigation. This work takes a top-down approach to accelerating decision support systems (DSS) on x86-64 microprocessors using vector ISA exten- sions. In the first step, a leading DSS DBMS is analysed for potential data-level parallelism. We discuss why the existing multimedia SIMD extensions (SSE/AVX) are not suitable for capturing this parallelism and propose a complementary instruction set reminiscent of classical vector architectures. The instruction set is implemented using unin- trusive modifications to a modern x86-64 microarchitecture tailored for DSS DBMS. The ISA and microarchitecture are evaluated using a cycle-accurate x86-64 microarchitectural simulator coupled with a highly-detailed memory simulator. We have found a single oper- ator is responsible for 41% of total execution time for the TPC-H DSS benchmark. Our results show performance speedups between 1.94x and 4.56x for an implementation of this operator run with our proposed hardware modifications. 2013-05-16T09:15:37Z http://hdl.handle.net/2117/19275 Title: Automatic refinement of parallel applications structure detection Authors: González, Juan; Huck, Kevin; Giménez Lucas, Judit; Labarta Mancho, Jesús José Abstract: Analyzing parallel programs has become increasingly difficult due to the immense amount of information collected on large systems. In this scenario, cluster analysis has been proved to be a useful technique to reduce the amount of data to analyze. A good example is the use of the density-based cluster algorithm DBSCAN to identify similar single program multiple data (SPMD) computing phases in message-passing applications. This structure detection simplifies the analyst work as the whole information available is reduced to a small set of clusters. However, DBSCAN presents two major problems: it is very sensitive to its parametrization and is not capable of correctly detect clusters when the data set has different densities across the data space. In this paper, we introduce the Aggregative Cluster Refinement, an iterative algorithm that produces more accurate structure detections of SPMD phases than DBSCAN. In addition, it is able to detect clusters with different densities 2013-05-16T08:57:41Z http://hdl.handle.net/2117/18559 Title: Integrating dataflow abstractions into the shared memory model Authors: Gajinov, Vladimir; Stipic, Srdjan; Unsal, Osman Sabri; Harris, Tim; Ayguadé Parra, Eduard; Cristal Kestelman, Adrián Abstract: In this paper we present Atomic Dataflow model (ADF), a new task-based parallel programming model for C/C++ which integrates dataflow abstractions into the shared memory programming model. The ADF model provides pragma directives that allow a programmer to organize a program into a set of tasks and to explicitly define input data for each task. The task dependency information is conveyed to the ADF runtime system which constructs the dataflow task graph and builds the necessary infrastructure for dataflow execution. Additionally, the ADF model allows tasks to share data. The key idea is that comput ation is triggered by dataflow between tasks but that, within a task, execution occurs by making atomic updates to common mutable state. To that end, the ADF model employs transactional memory which guarantees atomicity of shared memory updates. We show examples that illustrate how the programmability of shared memory can be improved using the ADF model. Moreover, our evaluation shows that the ADF model performs well in comparison with programs para llelized using OpenMP and transactional memory. 2013-04-03T10:24:08Z http://hdl.handle.net/2117/18558 Title: On the instrumentation of OpenMP and OmpSs Tasking constructs Authors: Servat, Harald; Teruel, Xavier; Llort Sanchez, German; Duran, Alejandro; Giménez, J.; Martorell Bofill, Xavier; Ayguadé Parra, Eduard; Labarta Mancho, Jesús José Abstract: Parallelism has become more and more commonplace with the advent of the multicore processors. Although different parallel pro- gramming models have arisen to exploit the computing capabilities of such processors, developing applications that take benefit of these pro- cessors may not be easy. And what is worse, the performance achieved by the parallel version of the application may not be what the developer expected, as a result of a dubious ut ilization of the resources offered by the processor. We present in this paper a fruitful synergy of a shared memory parallel compiler and runtime, and a performance extraction library. The objective of this work is not only to reduce the performance analysis life-cycle when doing the parallelization of an application, but also to extend the analysis experience of the parallel application by incorporating data that is only known in the compiler and runtime side. Additionally we present performance results obtained with the execution of instrumented application and evaluate the overhead of the instrumentation. 2013-04-03T10:14:57Z http://hdl.handle.net/2117/18498 Title: Accelerating boosting-based face detection on GPUs Authors: Oro, David; Fernández, Carles; Segura, Carlos; Martorell Bofill, Xavier; Hernando Pericás, Francisco Javier Abstract: The goal of face detection is to determine the presence of faces in arbitrary images, along with their locations and dimensions. As it happens with any graphics workloads, these algorithms benefit from data-level parallelism. Existing parallelization efforts strictly focus on mapping different di- vide and conquer strategies into multicore CPUs and GPUs. However, even the most advanced single-chip many-core pro- cessors to date are still struggling to effectively handle real- time face detection under high-definition video workloads. To address this challenge, face detection algorithms typically avoid computations by dynamically evaluating a boosted cascade of classifiers. Unfortunately, this technique yields a low ALU occupancy in architectures such as GPUs, which heavily rely on large SIMD widths for maximizing data-level parallelism. In this paper we present several techniques to increase the performance of the cascade evaluation kernel, which is the most resource-intensive part of the face detection pipeline. Particularly, the usage of concurrent kernel execution in combination with cascades generated with the GentleBoost algorithm solves the problem of GPU underutilization, and achieves a 5X speedup in 1080p videos on average over the fastest known implementations, while slightly improving the accuracy. Finally, we also studied the parallelization of the cascade training process and its scalability under SMP platforms. The proposed parallelization strategy exploits both task and data-level parallelism and achieves a 3.5X speedup over single-threaded implementations 2013-03-22T13:12:26Z http://hdl.handle.net/2117/18360 Title: Task-based parallel breadth-first search in heterogeneous environments Authors: Munguía, Lluis Miquel; Bader, David A.; Ayguadé Parra, Eduard Abstract: Breadth-first search (BFS) is an essential graph traversal strategy widely used in many computing applications. Because of its irregular data access patterns, BFS has become a non-trivial problem hard to parallelize efficiently. In this paper, we introduce a parallelization strategy that allows the load balancing of computation resources as well as the execution of graph traversals in hybrid environments composed of CPUs and GPUs. To achieve that goal, we use a fine-grained task-based parallelization scheme and the OmpSs programming model. We obtain processing rates up to 2.8 billion traversed edges per second with a single GPU and a multi-core processor. Our study shows high processing rates are achievable with hybrid environments despite the GPU communication latency and memory coherence. 2013-03-18T10:13:40Z http://hdl.handle.net/2117/18339 Title: Introducing speculative optimizations in task dataflow with language extensions and runtime support Authors: Azuelos, Nathaniel; Etsion, Yoav; Keidar, Idit; Zaks, A.; Ayguadé Parra, Eduard Abstract: We argue that speculation leads to increased parallelism in the coarse-grain dataflow paradigm. To do so, we present a framework for adding speculation in a popular and well-established framework. We specify a limited set of additions to the OmpSs language and changes required in its supporting runtime environment. These modifications enable speculation across the system in a flexible way. We evaluate our implementation using a simple benchmark leading to a promising 10% speedup. 2013-03-15T10:54:59Z http://hdl.handle.net/2117/18335 Title: Optimizing resource utilization with software-based temporal multi-threading (sTMT) Authors: Beltran Querol, Vicenç; Ayguadé Parra, Eduard Abstract: Compute and memory access units are two of the most important resources to appropriately manage in current and future multi–/many–core architectures. Memory bandwidth and computational capacity need to be exploited in a combined way to achieve the best system performance. Coarse–grain multi– threading, also known as temporal multi–threading (TMT), is a well known technique that improves overall resource utilization by time–multiplexing the execution of a reduced number of hardware threads that are switched in case of a high–latency event, such as a memory miss. Hence, the processor does not stall on memory misses and the number of in–fly memory operations is increased, improving the overall processor resource utilization. In this paper, we propose a software–based implementation of TMT that supports and unbounded number of threads and enables a flexible combination of multiple computational kernels. Our TMT implementation is based on micro–threads that combine fast cooperative and preemptive context switches to overcome some intrinsic limitations of current TMT hardware implementations, such as the reduced and fixed number of hardware threads available. Our proposal is demonstrated with an implementation on the Cell/B.E. which is evaluated using heterogeneous mixes of memory–/CPU–bound kernels. Experimental results show how the proposed technique reduce the execution time of several benchmarks by up to 78%. 2013-03-15T09:57:14Z http://hdl.handle.net/2117/18039 Title: All-terminal reliability evaluation through a Monte Carlo simulation based on an MPI implementation Authors: Pascual Martinez, Silvia; Otero Calviño, Beatriz; Rocco Sanseverino, Claudio M. Abstract: All-terminal reliability (ATR), defined as the probability that every node in a network can communicate with every other node, is an important problem in research areas such as mobile ad-hoc wireless networks, grid computing systems, and telecommunications. The assessment of ATR has also been part of related problems like the reliability allocation problem. However, the exact calculation of ATR is a NP-hard problem. To obtain this probability, there are approaches based on analytic methods for small networks or estimation through Monte Carlo simulation (MCS). In this paper, a parallel MCS implementation, based on the Message Passing Interface (MPI) standard is presented. The implementation can take advantage of the existence of multiprocessor thus reducing the time required for the ATR assessment. Three examples related to real network illustrate the benefits. 2013-03-04T11:04:27Z http://hdl.handle.net/2117/17882 Title: Implementation of Web 2.0 Tools and Virtual Platforms to PBL Methodology: a Case Study Authors: Cusso Calabuig, Roser; Gil, Marisa Abstract: In problem-based learning (PBL), students work together in groups to solve real-world problems. This is a very promising methodology to prepare students for 21st century skills as leadership and think critically, and to develop a model for lifelong learning. Furthermore the rise of Web 2.0 as a collaborative platform offering a wide range of communication and website-based tools fits very well with this PBL learning mode. In this paper, we present a real experience supporting this thesis in a high school. The project has been possible thanks to the Educat 2.0 project in Catalonia schools that provides the technical infrastructure suitable for schools, teachers and mainly students to easily access internet and Web 2.0 tools. 2013-02-19T14:06:14Z http://hdl.handle.net/2117/17721 Title: Client classification policies for SLA negotiation and allocation in shared cloud datacenters Authors: Macías Lloret, Mario; Guitart Fernández, Jordi Abstract: In Utility Computing business model, the owners of the computing resources negotiate with their potential clients to sell computing power. The terms of the Quality of Service (QoS) to be provided as well as the economic conditions are established in a Service-Level Agreement (SLA). There are situations in which providers must differentiate the SLAs in function of the type of Client that is willing to access the resources or the agreed QoS e.g. when the hardware resources are shared between users of the company that own the resources and external users. This paper proposes to consider the information of potential users when the SLA is under negotiation to allow providers to prioritize users (e.g. internal users over external users, or preferential users over common users). Two policies for negotiation are introduced: price discrimination and client-aware overselling of resources. The validity of the policies is demonstrated through exhaustive experiments. 2013-02-13T13:29:55Z http://hdl.handle.net/2117/17650 Title: Using a crowdsourcing knowledge base to support the Sustainability and Social Compromise skill in Computer Science Engineering studies Authors: Alier Forment, Marc; López Álvarez, David; Sánchez Carracedo, Fermín; García Almiñana, Jordi; Piguillem Poch, Jordi; Velasco Becerra, Martha Elena Abstract: The Skill "Sustainability and Socia Commitment" is commonly accepted as essential in today's world. However it proves tricky to introduce into the curriculum, mainly because of lack of knowledgeable teachers. To address this issue we present a knowledge base that brings together scientific articles, books, videos, compilations of data, experiences, etc., related to sustainability and knowledge areas associated with computer science engineering. This is a valuable tool that should provide to the teacher accurate and useful information in the research task of finding links between her course and the "Sustainability and Social Commitment" skill. 2013-02-12T11:51:24Z