TERRA-NEO - Integrated Co-Design of an Exascale Earth Mantle Modeling Framework

人们所说的地球的地质活动，很大程度上是由于这样一个事实，即热量通过地幔在全球范围内的固态对流，从地球内部传递到地表。将地幔过程与其地表表现联系起来，今天被广泛视为地球科学中最基本的问题之一，同时由于它们对沉积盆地演化的影响及其最重要的经济意义，也是一个直接实际相关的问题。从学科复杂性的急剧增长可以很容易地把握现代超级计算机体系结构中地幔模拟的计算挑战的绝对规模。地球物理学的主要障碍是模型的复杂性和参数和数据的不确定性，例如流变学和地震成像的地幔非均质性，以及必须解决的巨大空间和时间尺度。在算法方面，传统的最优性观点越来越过时，必须被新的高性能计算性能导向指标所取代。在百亿亿次计算中，从适度并发到数十亿线程的颠覆性转变使软件开发落后于人。该联盟已经通过一系列联合出版物展示了跨学科研究的潜力，参见B部分第1.1小节，并且完全致力于将TERRA-NEO创建为新的社区可用的、可持续的百亿亿次模拟框架所必需的跨学科合作。新的社区代码TERRA-NEO将基于精心设计的多尺度有限元离散化，使用二十面体网格进行分块细化，用于地球地幔的非线性传输过程。这允许构建具有最大可扩展性和最佳效率的百亿亿次求解器。我们已经在千万亿次超级计算机上演示了流场的计算，其全球分辨率为1km，这在最近之前是不可想象的，因为它需要解决每个时间步长超过10到12个未知数的不确定系统。推进到百亿亿级，我们将开发避免通信的异步解决技术，以减轻传统的分层迭代方法的过度同步，使反问题的解决和不确定性的量化成为可能。先进的弹性技术将在算法层面得到支持。TERRA-NEO将专门为即将到来的异构百亿亿次计算机开发，其架构感知设计过程由性能模型指导，导致数据结构和算法的整体协同设计。

Much of what one refers to as geological activity of the Earth is due to the fact that heat is transported from the interior of our planet to the surface in a planetwide solid-state convection of the Earth's mantle. Linking mantle processes to their surface manifestations is seen widely today as one of the most fundamental problems in the Earth sciences, while being at the same time a matter of direct practical relevance through their impact on the evolution of sedimentary basins and their paramount economical importance.The sheer magnitude of the computational challenge of earth mantle simulations on modern super- computer architectures can be grasped easily from the dramatic growth of disciplinary complexity. Dominating roadblocks in Geophysics are model complexity and uncertainty in parameters and data, e.g., rheology and seismically imaged mantle heterogeneity, as well as the enormous space and time scales one must resolve. In Algorithmics, the traditional view of optimality is more and more obsolete and must be replaced by new HPC performance oriented metrics. In Exascale Computing, the disruptive transition from modest concurrency to billions of threads leaves the software devel- opment trailing behind. This consortium has already demonstrated the potential of interdisciplinary research by a series of joint publications, see Part B Subsection 1.1, and is fully committed to the cross-disciplinary collaboration that is necessary for creating TERRA-NEO as new community-usable, sustainable exascale simulation framework.The new community code TERRA-NEO will be based on a carefully designed multi-scale finite ele- ment discretization using an icosahedral mesh with block-wise refinement for the non-linear trans- port processes in the Earth mantle. This permits the construction of exascale solvers with maximal scalability and optimal efficiency. We have already demonstrated the computation of flow fields on petascale supercomputers with a resolution of globally 1km that would have been unthinkable until recently since it requires the solution of indefinite systems of more than 10 to the 12 unknowns per time step.Advancing to exascale, we will develop communication-avoiding, asynchronous solution techniques that alleviate the traditional over-synchronization of hierarchical iterative methods, enabling the solution of inverse problems and the quantification of uncertainties. Advanced resiliency techniques will be supported on the algorithmic level. TERRA-NEO will be developed specifically for the upcoming heterogeneous exascale computers in an architecture-aware design process that is guided by performance models, leading to a holistic co-design of the data structures and algorithms.