As the US Department of Energy (DOE) computing facilities began deploying petascale systems in 2008, DOE was already setting its sights on exascale. In that year, DARPA published a report on the feasibility of reaching exascale. The report authors identified several key challenges in the pursuit of exascale including power, memory, concurrency, and resiliency. That report informed the DOE's computing strategy for reaching exascale. With the deployment of Oak Ridge National Laboratory's Frontier supercomputer, we have officially entered the exascale era. In this paper, we discuss Frontier's architecture, how it addresses those challenges, and describe some early application results from Oak Ridge Leadership Computing Facility's Center of Excellence and the Exascale Computing Project.

This paper presents new advances in GPU-driven Fourier pseudo-spectral numerical algorithms, which allow the simulation of turbulent fluid flow at problem sizes beyond the current state of the art. In contrast to several massively parallel petascale systems, the dense nodes of Summit, Sierra, and expected exascale machines can be exploited with coarser MPI decompositions which result in improved MPI all-to-all scaling. An asynchronous batching strategy, combined with the fast hardware connection between the large CPU memory and the fast GPUs allows effective use of the GPUs on problem sizes which are too large to reside in GPU memory. Communication performance is further improved by a hybrid MPI+OpenMP approach. Favorable performance is obtained up to a 184323 problem size on 3072 nodes of Summit, with a GPU to CPU speedup of 4.7 for a 122883 problem size (the largest problem size previously published in turbulence literature).