11 Brian Van Straalen Portable Performance Discussion August 7, FASTMath SciDAC Institute

22  C/C++11 will run on all systems correctly C++ std::thread might not be performant for several more years  Fortran 2003 should be working everywhere. Fortran 2008 might be available  CoArrays, DO CONCURRENT  MPI will be available on CPUs  CPU-based machines will have some form of threading OpenMP is the current expected flavor.  GPU accelerator machines will support a kernel offload style of computing through CUDA or OpenCL.  C/C++/CUDA/OpenCLFortran will link together correctly First, the portable and performant basics

33  Multicore CPU compute nodes (Cray XC30, XC40)  Multicore CPU host with NVIDIA Accelerator (XE6, XK6, PowerEdge) host and accelerator connected by PCIe bus  Early Manycore hosted platforms (BG/Q). Higher count of simpler cores Current hardware landscape

44  Developers With the minimum amount of code divergence capture as much of the available performance on a the range of target architectures.  Users Application parallelism and library parallelism not mandated  MPI Endpoints a possible way for MPI+X to work with flat MPI. Users can decide to adopt a library’s programming model and build environment.  It is hard to not subject Users to the Library data structure choices. Developers vs Users

55  MPI3+OpenMP4 as a portable programming model Department of Energy vendors recommended BoxLib already uses MPI2+OpenMP3  MPI3 More asynchronous styles available One-sided communication Fewer dynamic load-balancing options than threads default private address spaces  OpenMP4 threading, SIMD vector and offload kernel directives Move towards code generator for OpenMP code  More I/O abstractions Chombo is going to drink the Kool-aid

66  On-core networking and off-core networking will start to merge. System-On-Chip designs are more energy efficient NIC-on-chip is already on the roadmap.  NIC and On-Chip are merging.  Intel: Sherkar Borkar: Sending messages using source and destination addresses would be the most efficient and sensible approach because all of the hardware necessary to accomplish it is already present.  NVIDIA: Steve Oberlin :We can make hardware to accelerate matching for MPI, but it is redundant hardware given address matching logic is already in there  MPI Tag matching is ulcer-inducing for next generation hardware designers  Heterogenous compute resources but Unified Memory Unified, but certainly not Uniform  Chombo will be minimizing reliance on MPI semantics What convergence of hardware can we expect?