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Descripción
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| Reducing and controlling the energy consumption and the environmental impact of computing technologies have become a challenging problem worldwide. It is a significant issue in systems ranging from small Internet of Things devices, sensors, smart watches, smart phones and portable/implantable medical devices, to large data centers and high-performance computing systems. In spite of the recent rapid advances in energy-efficient hardware, including battery and energy harvesting technology, it is software that controls the hardware, so that the greatest savings are expected from developing software applications that perform a better management of the energy-saving features and resources provided by the hardware. For a given system, the potential for energy savings is likely to be much greater at the higher levels of abstraction in the system stack. Thus, promoting energy efficiency to a first class software design goal has become an important research challenge. This thesis addresses this challenge and provides tools and techniques for energy-aware software development. First, the thesis focuses on the development of techniques for the estimation of lower and upper bounds on the energy consumed by software applications, as well as the verification that such applications meet some energy budgets (given as specifications). Addressing a challenging objective, such techniques perform the estimations statically (i.e., at compile-time, without running the program with concrete data), and give such information in the form of functions on the input data sizes of programs (and possibly other parameters, such as clock frequency, voltage, etc.). The proposed approach performs a combination of techniques for static program analysis with techniques for modeling hardware platforms. The energy models are used to represent the effect, regarding energy consumption on the hardware, of running basic software elements (e.g., low-level assembly instructions or blocks). The static analysis propagates such information through code segments, conditionals, loops, recursions, etc., in order to infer the energy consumption of the whole program. One of the main contributions of the thesis is a multi-language general resource consumption analysis, and a specialization that infers both lower- and upper-bound energy functions at two levels, the Instruction Set Architecture (ISA) and the intermediate code (LLVM IR) levels, and reflects them upwards to the higher source code level. To achieve this, we develop translations from both ISA and the LLVM IR to an intermediate representation (Horn clauses) on which the analysis operates on. Another contribution is the experimental assessment of such analysis, which provides insights into the trade-off of accuracy versus analyzability at these levels, and concludes that the LLVM IR level analysis is a good compromise: it is reasonably powerful and accurate (less than 6.4% average deviation vs. hardware measurements). The analysis estimates safe lower and upper bounds on the use of resources that are independent from the hardware, such as execution steps. However, in order to infer safe bounds for hardware-dependent resources, such as energy, the analysis needs to be fed with energy models that provide safe bounds too. To this end, the thesis proposes a novel modeling approach that consists in dividing a program into basic (branchless) blocks, establishing the maximal (resp. minimal) energy consumption for each block using an evolutionary algorithm. Then, such block-level model is used by the static analysis to infer tight energy bounds that are practical for energy verification and optimization applications. The approach has been tested on XC programs running on XMOS chips, but it is general enough to be applied to any microprocessor and programming language. The experimental results show that the bounds obtained by our prototype tool can be tight while remaining on the safe side of actual energy consumption in practice | |
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Internacional
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ISBN
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Tipo de Tesis
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Doctoral |
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Calificación
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Aprobado |
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Fecha
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04/07/2018 |