Performance-optimized co-design of ocean modeling software on FPGAs

现代洪水/天气/气候预测模型严重依赖于复杂的数值方法和不断增加的空间和时间分辨率，以提供更准确和物理全面的模拟。此外，更详细的物理和更复杂的数值方案更好地代表亚网格规模效应当然是议程的重点。然而，在地球甚至区域大小的域上运行高分辨率模型，对现代和未来的并行和混合架构上的模型代码的计算和能源效率提出了很高的要求。特别是，具有节能FPGA加速器和特殊的面向数据流的执行模型的HPC系统提供了特殊的潜力，但也需要全新的地球系统模型软件开发方法。在这个项目中，我们建议通过将计算机科学，数值算法和网格生成的几种创新方法结合在一个全面的软件/硬件协同设计概念中，从而大大提高技术水平，以提供以前无法实现的计算和能源性能水平。拟议的工作广泛利用了Aizinger教授和Grosso博士之间以及Kenter博士和Aizinger教授之间现有合作范围内创建的技术和工具。该项目的重点应用是一个海洋模型，它结合了地球物理和气候应用的一些关键物理、数学和数值方面。这些包括非常大的、几何上复杂的域，需要高精度的数值方法、重要物理量的局部守恒、低数值扩散、支持非结构化网格和良好的并行化特性。提出的项目的关键组成部分是：基于UTBEST代码的FPGA优化的不连续Galerkin （DG）求解器，独特组成的块结构网格-支持有或没有内部结构的块- DFG GR 1107/3-1中首次引入的方法的进一步发展，以及利用OpenCL并针对这种组合块网格进行优化的~数据流FPGA设计。开发的方法和技术将以技术演示（开放获取）的形式实施，并应用于高分辨率网格上的现实展示洪水场景。除了具体的示范之外，我们认为，这种综合跨学科工作的成功具有重要的方法附加值，可以随后在该领域和相关领域形成更雄心勃勃的项目，同时也为参与此类项目建立制度基础。

Modern flooding/weather/climate prediction models critically rely on sophisticated numerical methods and ever increasing spatial and temporal resolution to deliver more accurate and physically comprehensive simulations. Also more detailed physics and more complex numerical schemes better representing subgrid scale effects are certainly high on the agenda. However, running high-resolution models on planet- or even region-sized domains sets a very high bar for the computational and energy efficiency of model codes on modern and future parallel and hybrid architectures. In particular, HPC systems with energy-efficient FPGA accelerators and special data-flow-oriented execution models offer special potential, but also require completely new approaches for the software development of earth system models.With this project, we propose to substantially advance the state of the art by combining several innovative methodologies from computer science, numerical algorithms, and grid generation within a comprehensive software/hardware co-design concept to deliver previously unattainable computational and energy performance levels. The proposed work extensively utilizes the techniques and tools created in the scope of the existing cooperations between Prof. Aizinger and Dr. Grosso and between Dr. Kenter and Prof. Aizinger.The application in the focus of the project is an ocean model that combines a number of key physical, mathematical, and numerical aspects specific to geophysical and climate applications. These include very large, geometrically complex domains which require numerical methods with high accuracy, local conservation of important physical quantities, low numerical diffusion, support of unstructured meshes, and good parallelization properties. The key ingredients of the proposed project are: An FPGA-optimized discontinuous Galerkin (DG) solver based on the UTBEST code, block-structured meshes of unique makeup -- supporting blocks with and without inner structure -- a further development of methodology first introduced in DFG GR 1107/3-1, and a~data flow FPGA design utilizing OpenCL and optimized for such combined block meshes.The developed methodologies and techniques will be implemented in the form of a technology demonstrator (open access) and applied to realistic showcase flooding scenarios on a high resolution mesh. Beyond the concrete demonstrator, a success of this integrative inter-disciplinary work has, in our opinion, a significant methodological added value that can subsequently shape more ambitious projects in this and related areas, while also establishing the institutional foundations for participation in such projects.