HIGH PERFORMANCE COMPUTING Twenty years of the OpenMP API
Michael Klemm, CEO, and Matthijs van Waveren, marketing coordinator for the OpenMP ARB, along with Jim Cownie, principal engineer, Intel Corporation (UK), consider the development of OpenMP over the last 20 years
The first version of the OpenMP application programming interface (API) was published in October 1997. That was the year when Dolly the sheep was born, the first Harry Potter book was published, and the Mars Pathfinder landed. The number one machine in the Top500 list was ASCII Red built from 1,952 Intel Pentium Pro 200MHz cores delivering 1.34 Tflops. What a year! In the 20 years since then, the OpenMP API and the slightly older MPI have become the two stable programing models that high-performance parallel codes rely on. MPI handles the message passing aspects and allows code to scale out to significant numbers of nodes, while the OpenMP API allows programmers to write portable code to exploit the multiple cores and accelerators in modern machines. In this article, we’ll run
through the history of the OpenMP API and describe its evolution. From the very start, the OpenMP programming model has supported the changing architectures of modern machines, while remaining the stable and vendor-neutral programming model that is most relevant in the age where the number one machine in the Top500 now has over 10 million cores running at 1.45GHz delivering 125,436 Tflops. If you live in Europe (or even if you don’t!) it’s likely your weather forecast is created with the help of OpenMP, since both the IFS code used at the European Centre for Medium Range Weather Forecasting and the unified model at the UK Met Office use OpenMP directives.
What is the OpenMP API? The OpenMP API is a directive- based high-level programming model for shared-memory parallelism. It enables programmers to write regular C/C++ or Fortran code and augment it with directives that tell the compiler how to
transform the sequential code into a parallel version that smoothly executes in a multi- threaded environment. From its very beginning the OpenMP API provided a high-level programming model that allows for easy access to the parallel world, but also gave programmers who focus on gaining the last bit of performance, a path to high performance by exposing control over how the code is transformed. This vision continued throughout the past 20 years, adding features like tasking for irregular parallel applications, heterogeneous programming (sometimes referred to as “offloading”) for coprocessors, and support for single-instruction multiple- data machines.
”From its very beginning, the OpenMP API provided a high- level programming model”
Evolution of the OpenMP Specification The parallel programming world in 1997, when the OpenMP API was born, was different from what we experience today. Back then, systems had a central shared memory and two or more homogeneous CPUs that typically consisted of multiple chips. Each hardware vendor had their own way of programming these systems, which made the task of moving an HPC application from one system to another expensive. It was the OpenMP programming model that became the most widely accepted standard after it was published in 1997. Its success built on support from vendors and user communities, because it provided easy access to the performance of the multi- threaded world.
Summary of the Evolution of the OpenMP API Specification The OpenMP Architecture Review Board (ARB), set up to maintain and promote
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Key developments of the last 20 years 16 Scientific Computing World April/May 2017 @scwmagazine |
www.scientific-computing.com
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