1. FleCSI Applications, Ben Bergen & Hyun Lim, Los Alamos National Laboratory (10 minutes)The Flexible Computational Science Infrastructure (FleCSI) programming system provides a clutter-free environment that allows developers to focus on the arithmetic operations of their methods without the distraction of computer science details that are often visible in legacy simulation codes. To this end, FleSCI provides light-weight wrappers over the raw Kokkos interface that resemble native C++ keywords, e.g., forall. Using this design philosophy, we have been able to evolve our support to cover various Kokkos policies and execution spaces. HARD is a FleCSI-based application for radiation hydrodynamics that is performance portable across a variety of systems, e.g., El Capitan, Venado, and Crossroads, and inherits FleCSI’s support for multiple distributed-memory and tasking backends, e.g., Legion, HPX, and MPI. In this talk, we will demonstrate the basic data-parallel interface with implementation and usage examples. We will also present results for several test problems in inertial confinement fusion with comparisons between different backends and performance assessments in different heterogeneous computing environments.
2. DDC: A Performance Portable Library Abstracting Computation on Discrete Domains, Thomas Padioleau, CEA Paris-Saclay (10 minutes)The Discrete Domain Computation (DDC) library is a modern C++ library that aims to offer to the C++ world an equivalent to the xarray.DataArray Python environment. The Xarray library introduces labeled multidimensional arrays, enabling more intuitive data manipulation by associating dimensions with user-provided names rather than relying on positional indexing. This approach simplifies indexing, slicing, and broadcasting while reducing common indexing errors. Inspired by these ideas, DDC extends the Kokkos library providing zero-overhead dimension labeling for multidimensional arrays along with performance-portable multidimensional algorithms. This labeling mechanism enables compile-time detection of indexing and slicing errors, ensuring safer and more expressive array operations in C++. In this presentation, we will introduce the core concepts of DDC and demonstrate its usage through a simple example that highlights its key features.
3. TChem-atm - A Performance Portable Chemistry Solver for Atmospheric Chemistry, Oscar Diaz-Ibarra, Sandia National Laboratories (20 minutes)TChem-atm (
https://github.com/PCLAeroParams/TChem-atm) is a performance-portable software library designed to support atmospheric chemistry applications, specifically computing source term Jacobian matrices. The software utilizes Kokkos as its portability layer, preparing it for next-generation computing architectures. The software interface employs a hierarchical parallelism design to leverage the massive parallelism available on modern computing platforms, including model parallelism, batch parallelism, and nested parallelism for each problem instance. Additionally, TChem-atm is designed to be coupled with third-party libraries that may be used to advance the state of gas and particle species over time, notably interfacing with the Tines, Kokkos-kernels, and Sundials libraries. We have tested TChem-atm in two scenarios: using a typical reaction mechanism in atmospheric science and an example involving multiple aerosol particles. This testing framework allows us to evaluate our code by varying the number of evaluations and the size of the source term (right-hand side). Finally, we report performance measurements using the CUDA, HIP, and OpenMP back ends.
4. GPU Porting of the TRUST CFD Platform with Kokkos, Rémi Bourgeois, French Atomic Energy Commission (CEA) (20 minutes)TRUST is a High Performance Computing thermohydraulic platform for Computational Fluid Dynamics developed at the French Atomic Energy Commission (CEA). This software is designed for massively parallel (MPI) simulations of conduction, incompressible single-phase, and Low Mach Number (LMN) flows with a Weakly-Compressible multi-species solver and compressible multi-phase flows. It is used as the basis for many specialised applications in the nuclear and new energy fields across CEA. The code is being progressively ported to support GPU acceleration (Nvidia/AMD/Intel) thanks to the Kokkos library, as it is one of the demonstrators of the CExA project. In this talk we will go over our experience using Kokkos to progressively port our large code base. We will cover our enabled GPU features and performances. We will mention some of the difficulties we encountered as well as the strategies we had to adopt that sometimes differ from standard good practices due to the specificity of our application.
5. Omega: Towards a Performance-portable Ocean Model using Kokkos, Maciej Waruszewski, Sandia National Laboratories (20 minutes)High-resolution simulations of the Earth system require resources available only on the world's largest supercomputers, which are increasingly based on GPUs. However, CPU-based systems are still frequently used to conduct simulations at coarse resolutions. To be able to take advantage of all compute platforms, we are developing Omega: the Ocean Model for E3SM Global Applications, a new ocean model written in C++ using Kokkos for performance portability. Omega will replace MPAS-Ocean to become the new ocean component of the DOE’s Energy Exascale Earth System Model (E3SM). Omega is an unstructured mesh ocean model based on the same finite-volume scheme as the current ocean component. Work on Omega began in 2023. Currently, Omega is a layered shallow water model with passive tracers. While still simple, this initial version can run on realistic size meshes and contains computational kernels representative of the full model horizontal numerics. After briefly describing Omega, this talk will go into our experiences with Kokkos and present initial performance results from a variety of compute platforms.)
