Interstellar: Using Halide's Scheduling Language to Analyze DNN Accelerators

We show that DNN accelerator micro-architectures and their program mappings represent specific choices of loop order and hardware parallelism for computing the seven nested loops of DNNs, which enables us to create a formal taxonomy of all existing dense DNN accelerators. Surprisingly, the loop transformations needed to create these hardware variants can be precisely and concisely represented by Halide's scheduling language. By modifying the Halide compiler to generate hardware, we create a system that can fairly compare these prior accelerators. As long as proper loop blocking schemes are used, and the hardware can support mapping replicated loops, many different hardware dataflows yield similar energy efficiency with good performance. This is because the loop blocking can ensure that most data references stay on-chip with good locality and the processing units have high resource utilization. How resources are allocated, especially in the memory system, has a large impact on energy and performance. By optimizing hardware resource allocation while keeping throughput constant, we achieve up to 4.2X energy improvement for Convolutional Neural Networks (CNNs), 1.6X and 1.8X improvement for Long Short-Term Memories (LSTMs) and multi-layer perceptrons (MLPs), respectively.Comment: Published as a conference paper at ASPLOS 202

Data reuse buffer synthesis using the polyhedral model

Current high-level synthesis (HLS) tools for the automatic design of computing hardware perform excellently for the synthesis of computation kernels, but they often do not optimize memory bandwidth. As accessing memory is a bottleneck in many algorithms, the performance of the generated circuit could benefit substantially from memory access optimization. In this paper, we present a method and a tool to automate the optimization of memory accesses to array data in HLS by introducing local memory tailored perfectly to store only the data that are used repeatedly. Our method detects data reuse in the source code of the algorithm to be implemented in hardware, selects and parameterizes data reuse buffers, and generates a register transfer level design of the data buffers and a matching loop controller that coordinates reuse buffers and datapath operations. Throughout this paper, the polyhedral representation is used extensively as it proves to be well suited for calculations on loop nests and data accesses. As a consequence, this paper is limited to affine programs which can be represented in this model. Experiments show that our method outperforms state-of-the-art academic and commercial HLS tools

High-performance and hardware-aware computing: proceedings of the first International Workshop on New Frontiers in High-performance and Hardware-aware Computing (HipHaC\u2708)

The HipHaC workshop aims at combining new aspects of parallel, heterogeneous, and reconfigurable microprocessor technologies with concepts of high-performance computing and, particularly, numerical solution methods. Compute- and memory-intensive applications can only benefit from the full hardware potential if all features on all levels are taken into account in a holistic approach

Efficient Hardware Design Of Iterative Stencil Loops

A large number of algorithms for multidimensional signals processing and scientific computation come in the form of iterative stencil loops (ISLs), whose data dependencies span across multiple iterations. Because of their complex inner structure, automatic hardware acceleration of such algorithms is traditionally considered as a difficult task. In this paper, we introduce an automatic design flow that identifies, in a wide family of bidimensional data processing algorithms, sub-portions that exhibit a kind of parallelism close to that of ISLs; these are mapped onto a space of highly optimized ad-hoc architectures, which is efficiently explored to identify the best implementations with respect to both area and throughput. Experimental results show that the proposed methodology generates circuits whose performance is comparable to that of manually-optimized solutions, and orders of magnitude higher than those generated by commercial HLS tools

Extracting Data-Level Parallelism in High-Level Synthesis for Reconfigurable Architectures

High-Level Synthesis (HLS) tools are a set of algorithms that allow programmers to obtain implementable Hardware Description Language (HDL) code from specifications written high-level, sequential languages such as C, C++, or Java. HLS has allowed programmers to code in their preferred language while still obtaining all the benefits hardware acceleration has to offer without them needing to be intimately familiar with the hardware platform of the accelerator. In this work we summarize and expand upon several of our approaches to improve the automatic memory banking capabilities of HLS tools targeting reconfigurable architectures, namely Field-Programmable Gate Arrays or FPGA\u27s. We explored several approaches to automatically find the optimal partition factor and a usable banking scheme for stencil kernels including a tessellation based approach using multiple families of hyperplanes to do the partitioning which was able to find a better banking factor than current state-of-the-art methods and a graph theory methodology that allowed us to mathematically prove the optimality of our banking solutions. For non-stencil kernels we relaxed some of the conditions in our graph-based model to propose a best-effort solution to arbitrarily reduce memory access conflicts (simultaneous accesses to the same memory bank). We also proposed a non-linear transformation using prime factorization to convert a small subset of non-stencil kernels into stencil memory accesses, allowing us to use all previous work in memory partition to them. Our approaches were able to obtain better results than commercial tools and state-of-the-art algorithms in terms of reduced resource utilization and increased frequency of operation. We were also able to obtain better partition factors for some stencil kernels and usable baking schemes for non-stencil kernels with better performance than any applicable existing algorithm

Enabling multi-threaded execution and improved memory access in fine-grain near-data processing systems

Orientador: Marco Antonio Zanata AlvesTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa : Curitiba, 08/07/2022Inclui referênciasÁrea de concentração: Ciência da ComputaçãoResumo: Aplicações que lidam com grandes quantidades de dados são cada vez mais populares. No entanto, as arquiteturas tradicionais centradas em computação estão mal equipadas para lidar com essas aplicatções, pois elas causam muito movimento de dados no sistema devido aos acessos de dados quase constantes. Isso leva a um processamento ineficiente, com longos tempos de execução e alto consumo de energia. Os problemas causados por essa disparidade são amplamente conhecidos como memory wall. A partir do final da década de 1990, a ideia de mover parte da computação para perto da memória, quando benéfico, começou a ser considerada. Este conceito tornou-se conhecido como processamento próximo à memória e ganhou mais atenção no início da década de 2010 com o advento da tecnologia de Through-Silicon Via (TSV), que permitiu a integração direta das lógicas de processamento e armazenamento de dados no mesmo chip. Memórias 3D, que integram verticalmente armazenamento e lógica, tornaram-se comercialmente disponíveis desde então e pesquisadores da área de arquitetura de computadores reagiram propondo muitos projetos que colocam elementos de processamento na camada lógica normalmente encontrada nesses dispositivos. Esta tese propõe a Vector-In-Memory Architecture (VIMA), uma arquitetura de processamento próximo à memória baseada em memória 3D que implementa o processamento na memória colocando unidades funcionais na camada lógica desses dispositivos. Nosso projeto usa unidades funcionais vetoriais e uma memória cache para armazenamento dedicado e avança o estado da arte implementando exceções precisas e permitindo multi-threading próximo aos dadosna memória. Simulamos a execução de várias aplicações orientadas a dados em nossa arquitetura e, nossos resultados mostram que o design proposto, que utiliza 1 core e a VIMA, é capaz de superar uma arquitetura tradicional moderna de 16 cores em pelo menos 2× ao lidar com grandes tamanhos de conjuntos de dados. Além disso, essa aceleração no tempo de execução é alcançada enquanto se reduz o consumo de energia em pelo menos 75% de acordo com nossas estimativas. Em comparação com um trabalho similar do estado da arte, a VIMA é capaz de reduzir o tempo de execução de aplicações que fazem streaming de dados em pelo menos 32%.Abstract: Applications that deal with large amounts of data are increasingly popular. However, traditional computation-centric architectures are ill-equipped to handle such applications as they cause much data movement across the system due to their near-constant data accesses. This leads to inefficient processing, with long execution times and high energy consumption. Issues caused by this disparity are widely known as the memory wall. Starting in the late 1990s, the idea of moving portions of the computations close to the memory when beneficial began to be considered. This concept has now become known as Near-Data Processing (NDP) and gained more attention in the early 2010s with the advent of TSV technology, which enabled straight-forward integration of processing logic and data storage in the same chip. 3D-stacked memories, which vertically integrate storage and logic, have become commercially available ever since and computer architecture researchers have reacted by proposing many designs that place processing elements on the logic layer typically found in those devices. This thesis proposes VIMA, a 3D-stacked memory-based NDP architecture that implements processing in the memory by placing Functional Units (FUs) on the logic layer of those devices. Our design uses a vector functional units and a cache memory for dedicated storage and advances the state-of-the-art by implementing near-data precise exceptions and enabling near-data multi-threading. We simulate execution of several common data-driven applications on our architecture and, out results show that the proposed design, with only a single processing core and VIMA, is able to outperform a modern 16-thread by at least 2× when dealing with large dataset sizes. Moreover, such a speedup in performance is achieved while reducing energy consumption by at least 75% according to our estimates. In comparison to its most closely related state-of-the-art work, VIMA is able to reduce the execution time of data-streaming applications by at least 32%

DAMOV: A New Methodology and Benchmark Suite for Evaluating Data Movement Bottlenecks

Data movement between the CPU and main memory is a first-order obstacle against improving performance, scalability, and energy efficiency in modern systems. Computer systems employ a range of techniques to reduce overheads tied to data movement, spanning from traditional mechanisms (e.g., deep multi-level cache hierarchies, aggressive hardware prefetchers) to emerging techniques such as Near-Data Processing (NDP), where some computation is moved close to memory. Our goal is to methodically identify potential sources of data movement over a broad set of applications and to comprehensively compare traditional compute-centric data movement mitigation techniques to more memory-centric techniques, thereby developing a rigorous understanding of the best techniques to mitigate each source of data movement. With this goal in mind, we perform the first large-scale characterization of a wide variety of applications, across a wide range of application domains, to identify fundamental program properties that lead to data movement to/from main memory. We develop the first systematic methodology to classify applications based on the sources contributing to data movement bottlenecks. From our large-scale characterization of 77K functions across 345 applications, we select 144 functions to form the first open-source benchmark suite (DAMOV) for main memory data movement studies. We select a diverse range of functions that (1) represent different types of data movement bottlenecks, and (2) come from a wide range of application domains. Using NDP as a case study, we identify new insights about the different data movement bottlenecks and use these insights to determine the most suitable data movement mitigation mechanism for a particular application. We open-source DAMOV and the complete source code for our new characterization methodology at https://github.com/CMU-SAFARI/DAMOV.Comment: Our open source software is available at https://github.com/CMU-SAFARI/DAMO

Techniques for optimizing dynamic parallelism on graphics processing units

Dynamic parallelism is a feature of general purpose graphics processing units (GPUs) whereby threads running on a GPU can spawn other threads without CPU intervention. This feature is useful for programming applications with nested parallelism where threads executing in parallel may each identify additional work that can itself be parallelized. Unfortunately, current GPU microarchitectures do not efficiently support using dynamic parallelism for accelerating applications with nested parallelism due to the high overhead of grid launches, the limited number of grids that can execute simultaneously, and the limited supported depth of the dynamic call stack. The compiler techniques presented herein improve the performance of applications with nested parallelism that use dynamic parallelism by mitigating the aforementioned microarchitectural limitations. Horizontal aggregation fuses grids launched by threads in the same warp, block, or grid into a single aggregated grid, thereby reducing the total number of grids launched and increasing the amount of work per grid to improve occupancy. Vertical aggregation fuses grids down the call stack with their descendant grids, again reducing the total number of grids launched but also reducing the depth of the call stack and removing grid launches from the application's critical path. Evaluation of these compiler techniques shows that they result in substantial performance improvement over regular dynamic parallelism for benchmarks representing common nested parallelism patterns. This observation has held true for multiple architecture generations, showing the continued relevance of these techniques. This work shows that to make dynamic parallelism practical for accelerating applications with nested parallelism, compiler transformations can be used to aggregate dynamically launched grids, thereby amortizing their launch overhead and improving their occupancy, without the need for additional hardware support