Fernando Alexandre

Algorithmic skeleton framework for the orchestration of GPU computations

The Graphics Processing Unit (GPU) is gaining popularity as a co-processor to the Central Processing Unit (CPU). However, harnessing its capabilities is a non-trivial exercise that requires good knowledge of parallel programming, more so when the complexity of these applications is increasingly rising. Languages such as StreamIt [1] and Lime [2] have addressed the offloading of composed computations to GPUs. However, to the best of our knowledge, no support exists at library level. To this extent, we propose Marrow, an algorithmic skeleton framework for the orchestration of OpenCL computations. Marrow expands the set of skeletons currently available for GPU computing, and enables their combination, through nesting, into complex structures. Moreover, it introduces optimizations that overlap communication and computation, thus conjoining programming simplicity with performance gains in many application scenarios. We evaluated the framework from a performance perspective, comparing it against hand-tuned OpenCL programs. The results are favourable, indicating that Marrows skeletons are both flexible and efficient in the context of GPU computing.

On the support of task-parallel algorithmic skeletons for multi-GPU computing

An emerging trend in the field of Graphics Processing Unit (GPU) computing is the harnessing of multiple devices to cope with scalability and performance requirements. However, multi-GPU execution adds new challenges to the already complex world of General Purpose computing on GPUs (GPGPU), such as the efficient problem decomposition, and dealing with device heterogeneity. To this extent, we propose the use of the Marrow algorithmic skeleton framework (ASkF) to abstract most of the details intrinsic to the programming of such platforms. To the best of our knowledge, Marrow is the first ASkF to support skeleton nesting on single and (now) multiple GPU systems. In this paper we present how it can transparently distribute the execution of skeleton compositions among a set of, possibly, heterogeneous devices. An experimental evaluation assesses the proposals effectiveness, from a scalability and performance perspective, with good results.

Towards the Transparent Execution of Compound OpenCL Computations in Multi-CPU/Multi-GPU Environments

Current computational systems are heterogeneous by nature, featuring a combination of CPUs and GPUs. As the latter are becoming an established platform for high-performance computing, the focus is shifting towards the seamless programming of the heterogeneous systems as a whole. The distinct nature of the architectural and execution models in place raise several challenges, as the best hardware configuration is behavior and data-set dependent. In this paper, we focus the execution of compound computations in multi-CPU/multi-GPU environments, in the scope of Marrow algorithmic skeleton framework, the only, to the best of our knowledge, to support skeleton nesting in GPU computing. We address how these computations may be efficiently scheduled onto the target hardware, and how the system may adapt itself to changes in the CPUs load and in the input data-set.

Execution of compound multi-kernel OpenCL computations in multi-CPU/multi-GPU environments

Current computational systems are heterogeneous by nature, featuring a combination of CPUs and graphics processing units (GPUs). As the latter are becoming an established platform for high‐performance computing, the focus is shifting towards the seamless programming of these hybrid systems as a whole. The distinct nature of the architectural and execution models in place raises several challenges, as the best hardware configuration is behavior and workload dependent. In this paper, we address the execution of compound, multi‐kernel, open computing language computations in multi‐CPU/multi‐GPU environments. We address how these computations may be efficiently scheduled onto the target hardware, and how the system may adapt itself to changes in the workload to process and to fluctuations in the CPUs load. An experimental evaluation attests the performance gains obtained by the conjoined use of the CPU and GPU devices, when compared with GPU‐only executions, and also by the use of data‐locality optimizations in CPU environments. Copyright

Emerging Models of Teacher Training: The Case of Portugal

Political/National Contexts for Changes The structural reforms of geography teacher training in Portugal have been justified by the global evolution of the educational system and took into account: (1) the political will to extend the period of compulsory schooling, which now covers the whole of lower secondary education, but will soon cover upper secondary education as well; (2) the inclusion of a growing proportion of pupils whose composition is socially, ethnically and culturally diversified; (3) the rising ‘massification’ of higher education, which has led to measures that have altered the branches of study, as well as the types of courses on offer, namely in Higher Schools of Education and private universities. Nevertheless, the number of students is now decreasing in both lower and upper secondary education (data from 2002/2003 point to a reduction of 2.6% and 5.0% respectively), which are precisely the school levels for which geography is an important curriculum subject. Thus, the evolution of schools’ demographic indicators is already causing a surplus in the whole supply of teachers for many curricular subjects and will surely affect geography teachers in a similar way. As a response to such conditions, major policy changes were recently introduced in recruitment methods, which make it difficult for newly qualified teachers to apply for a school place and secure permanent tenure. Until the mid-1980s, training was predominantly school based for all disciplines, although new forms of concurrent provision also began to be offered to prospective teachers in lower secondary education from 1971 and 1980 onwards. Such training was first given in the new educational training courses (ramos de formação educacional) of the science faculties, and was later extended to the arts faculties, where geography is integrated. Changes in society and the obligation of policy makers to adapt education to new demands seem unavoidable. How far these demands have an impact on the content of teacher training is therefore a question of utmost importance. Education authorities have tended to increase regulation of initial teacher training as part of tertiary-level educational provision. The reason for this trend may well be the desire for more uniform patterns of training, so that it corresponds to national and international quality standards. IRGEE 158g