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Idomura, Yasuhiro; Ina, Takuya*; Ali, Y.*; Imamura, Toshiyuki*
Proceedings of International Conference for High Performance Computing, Networking, Storage, and Analysis (SC 2020) (Internet), p.1318 - 1330, 2020/11
Times Cited Count：2 Percentile：47.53(Computer Science, Information Systems)The multi-scale full-
simulation of the next generation experimental fusion reactor ITER based on a five dimensional (5D) gyrokinetic model is one of the most computationally demanding problems in fusion science. In this work, a Gyrokinetic Toroidal 5D Eulerian code (GT5D) is accelerated by a new mixed-precision communication-avoiding (CA) Krylov method. The bottleneck of global collective communication on accelerated computing platforms is resolved using a CA Krylov method. In addition, a new FP16 preconditioner, which is designed using the new support for FP16 SIMD operations on A64FX, reduces both the number of iterations (halo data communication) and the computational cost. The performance of the proposed method for ITER size simulations with 0.1 trillion grids on 1,440 CPUs/GPUs on Fugaku and Summit shows 2.8x and 1.9x speedups respectively from the conventional non-CA Krylov method, and excellent strong scaling is obtained up to 5,760 CPUs/GPUs.
Idomura, Yasuhiro
no journal, ,
In this overview talk, first, we review computational nuclear engineering research activities at JAEA, which cover a wide spectrum of computing needs including various CFD codes on thermal hydraulics and environmental dynamics, radiation transport codes, quantum simulations on material science, and the latest machine learning applications. Second, we talk about the development of exascale nuclear CFD simulations on state-of-the-art accelerated computing platforms. Third, we present exascale plasma codes and new data science approaches developed under the post-K project. Finally, we discuss the state of the CEA-JAEA collaboration on computational nuclear engineering.
Idomura, Yasuhiro; Ali, Y.*; Ina, Takuya*; Imamura, Toshiyuki*
no journal, ,
Implicit finite difference solvers based on Krylov subspace methods occupy dominant computing costs in the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D. Under the post-K project, advanced communication avoiding (CA) Krylov subspace methods have been developed for exascale computing platforms, which have limited inter-node communication performance compared with accelerated computation. In this work, we develop a new mixed precision CA-GMRES solver using a FP16 preconditioner, which dramatically reduces the number of iterations, and thus, halo data communications. We port the new solver on FUGAKU and Summit, and compare its performance against conventional solvers on existing muti/many-core processors.
Idomura, Yasuhiro
no journal, ,
To study fusion plasma turbulence, the Gyrokinetic Toroidal 5D full-f Eulerian code GT5D has been developed. On the K-computer, inter-node parallelization techniques such as multi-dimensional/-layer domain decomposition and communication-computation overlap were developed, and strong scaling of GT5D was improved up to 73,728 nodes. However, extensions of GT5D towards burning plasmas including kinetic electrons and multi-species ions require greater computing power. Under the post-K project, we have developed computing techniques for the next generation platforms such as GPUs and MICs. In this talk, we discuss computational challenges related to complicated intra-node memory hierarchy on many core processors and relatively limited inter-node communication performance compared with accelerated computation.
Idomura, Yasuhiro
no journal, ,
In this talk, we review the current status of the sub-project D "Core design of fusion reactor" in the Priority Issue on Post-K computer (Accelerated Development of Innovative Clean Energy Systems). In the project, an interdisciplinary research team consisting of experts on applied mathematics, computer science, plasma theory, and plasma experiment has addressed (1) development of exascale computing technologies, (2) extension of physics models for burning plasmas, and (3) V&V of developed codes against large scale experiments such as JT-60 and LHD. Outcomes from the first two years of the project are presented focusing on computing techniques and physics models for analyzing multi time scale phenomena such as transient responses of plasma turbulence against auxiliary heating and intermittent bursts of energetic particles driven modes, and future issues in the latter half of the project.
Idomura, Yasuhiro
no journal, ,
The Gyrokinetic Toroidal 5D full-f Eulerian code GT5D is based on a semi-implicit finite difference scheme, in which a stiff linear 4D convection operator is subject to implicit time integration, and the implicit finite difference solver for fast kinetic electrons occupies more than 80% of the total computing cost. The implicit solver was originally developed using a Krylov subspace method, in which global collective communications and halo data communications were becoming bottlenecks on the latest accelerator based platforms. To resolve this issue, the convergence property is improved by using a new FP16 preconditioner, and an order of magnitude reduction of the number of iterations and thus, communications was achieved. A communication-avoiding (CA) solver based on the FP16 preconditioner was developed by utilizing the new support for FP16 SIMD operations on FUGAKU, and was ported also on Summit. The new CA solver showed significant speedups both on FUGAKU and SUMMIT, and its performance portability was demonstrated.
