XPS: FULL: FP: Tools and Algorithms for Resilient, Power-efficient ExaScale Computing Using the GNU-CAF Compiler

具有重大技术意义和深厚科学意义的各种问题都需要使用具有最高并行度的并行计算机。因此，科学界很好地认识到，这项研究需要在亿级计算机上进行，即计算能力比今天的计算机大1000倍的计算机。但扩大规模的技术努力伴随着几个随之而来的问题，比如能够重复使用现有代码，以及让普通开发人员能够编写可伸缩的软件，这些软件在功耗方面也是高效的，并且具有容错能力。这个项目通过提供一个开源(GNU许可的)、免费的FORTRAN编译器来满足这些需求，该编译器可以使现有代码准备好Exascale，并且允许只需要熟悉FORTRAN(并且有许多这样的语言)的程序员开发可伸缩、高能效和容错的代码，而不必学习过多的新编程技能。该项目还将有助于编写首席调查员正在编写的关于科学计算的教科书，以及正在由该小组另外两名研究人员编写的关于高性能计算的教科书。项目网站已经存在，将免费向公众传播此类知识。这个网站每年的点击量已经超过5万次。该提议将取得以下变革性的进展：1)开发一个成熟的、开源的、支持Exascale的GNU编译器，它实现了Fortran 2008标准的新的并行特性。这些Fortran功能以CoarrayFortran(CAF)的名称命名。最近的工作表明，CAF要么具有竞争力，要么性能优于最新的MPI-3标准，同时允许最终用户更简单地表达Petascale级并行性。未来的体系结构应该会使单边的CAF风格的消息传递与其他类型的消息传递相比不那么耗电。2)艾斯卡计算机将需要支持内核之间的十亿路并发，结果是节点可能会非常频繁地出现故障。必须将对故障的恢复能力内置于编译器技术和终端用户应用程序中。将在GNU编译器中实现故障恢复能力的早期实现，并将使用它来探索这些功能如何在一大类计算流体动力学(CFD)算法中工作。3)亿级应用程序也将不得不非常节俭地使用电力。这只能通过决定何时将资源集中在通信上以及何时将其集中在计算上来实现。需要新的算法，将相对适中的通信量与大量的计算量点缀在一起。此外，专家级算法开发人员应该能够通过编译器指令将这些不同的资源需求传递给运行时系统。这项拟议的工作将开发一类高精度的CFD算法，该算法可以通过GNU编译器中的编译器扩展将其资源需求传递给运行时系统。

Various problems of technological significance as well as of deep scientific interest require the use of parallel computers with the highest levels of parallelism. Thus, it is well-recognized in the scientific community that this research needs to be performed on Exascale computers, i.e. computers that have a thousand-fold greater computing power than computers today. But the technological endeavour of scaling-up comes with several attendant problems, such as being able to reuse existing code and giving the ability to ordinary developers to write scalable software that is also efficient with respect to power consumption, and is fault tolerant. This project addresses these needs by providing a open-source (GNU licensed), free, FORTRAN compiler that can make existing code Exascale ready, and which allows a programmer who only needs to be familiar with FORTRAN (and there are many of those) to develop scalable, power-efficient and fault-tolerant code, without having to learn an inordinate amount of new programming skills. The project will also contribute to a textbook on scientific computation that is being written by the Principal Investigator, as well as to a textbook on high performance computing that is being written by 2 other researchers on the team. The project website already exists that will freely distribute such knowledge to the public. This website already gets more than 50,000 hits per year. The proposal will make the following transformative advances:1) Develop a full-fledged, open-source, Exascale-Ready GNU compiler that implements novel parallel features of the Fortran 2008 standard. These Fortran features go under the name of Coarray Fortran (CAF). Recent work has shown that CAF is either competitive or outperforms the recent MPI-3 standard while allowing the end-user to express Petascale-class parallelism much more simply. Future architectures should make the one-sided CAF-style messaging much less power-hungry compared to alternative styles of messaging.2) Exascale computers will need to support billion-way concurrency among cores, with the result that nodes might fail quite frequently. Resiliency to failure will have to be built into the compiler technologies and end-user application. An early implementation of failure-resiliency within the GNU compiler will be made and it will be used to explore how those features work within a large class of Computational Fluid Dynamics (CFD) algorithms.3) Exascale applications will also have to use power very parsimoniously. This can only be done by deciding when to focus resources on communication and when to focus them on computation. New algorithms are needed that intersperse relatively modest amounts of communication with large amounts of computation. Furthermore, the expert-level algorithm developer should be able to communicate these different resource needs to the run-time system via compiler directives. The proposed work will develop a class of high-accuracy CFD algorithms that can communicate their resource needs to the run-time system via compiler extensions in the GNU compiler.