OpenFOAM on POWER8. Stretching the performance envelope. A White Paper by OCF

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1 OpenFOAM on POWER8 Stretching the performance envelope A White Paper by OCF

2 Executive Summary In this white paper, we will show that the IBM Power architecture provides a uniquely powerful platform for computational fluid dynamic simulations, in particular when combined with the open source OpenFOAM application and OCF's unique integration and support services. Illustrative benchmark results are provided in this document as proof points. If you are engaged in the fields of engineering and science, whether from a commercial or and academic perspective, and have requirement to simulate fluid flows, you will gain a deeper understanding of the benefits that OCF's OpenFOAM on POWER8 package can deliver. Introduction Computational fluid dynamic simulations remain a powerful tool in a wide range of engineering and scientific disciplines, including aerospace, automotive, power generation, chemical manufacturing, medical research, and astrophysics. For those serious about achieving the right results using CFD, the IBM Power platform offers performance benefits up to 3x better than the x86 platform. High performance computing expert OCF believes that OpenFOAM running on IBM s POWER8 server offers the right combination of performance, reliability and cost-effectiveness, especially when combined with OCF s unique integration service and support offering, which brings together the benefits of OpenFOAM with the high performance of POWER8, for faster, more reliable modelling.

3 The power and the pain The OpenFOAM (Open Field Operation and Manipulation) CFD Toolbox is a free, open source CFD software package with a large user base across most areas of engineering and science, from both commercial and academic organisations. It offers a wide range of features to solve anything from complex fluid flows involving chemical reactions, turbulence and heat transfer, to solid dynamics and electro-magnetics. As with all CFD applications, reliability and performance are key. Calculating the millions of data points involved in simulating reality at high resolutions consumes vast amounts of computation time. It is not uncommon for simulations to take days or even longer to run. In a world where achieving a faster time to market is key and can be business-critical, this is a huge bottleneck in the process. A variety of factors influence computation time for example time step size, under relaxation factors (URF) or discretisation parameters but there is a limit to how much these parameters can be adjusted before simulation results no longer meet quality requirements. OCF s POWER8 solution Ultimately, the performance of a CFD simulation using OpenFOAM is heavily dependent on the quality and performance of the underlying hardware. IBM Power Systems are designed for big data and deliver the performance and throughput of POWER8 combined with the cost savings that the use of industry standards can bring. The Power S822LC server delivers high application performance and throughput based on its built-for-big-data architecture incorporating POWER8 processors, tightly coupled FPGAs and accelerators, and faster I/O using CAPI. It delivers more processing power while increasing workload density and reducing floor space requirements, and offers a modular design to scale from a single rack to hundreds, simplicity of ordering, and a strong innovation roadmap for GPUs. At the heart of the Power S822LC server is IBM s POWER8 processor. It consists of a family of superscalar symmetric multi-processors based on the Power architecture, designed to be a massively multi-threaded chip. Each core can handle eight hardware threads simultaneously, for a total of 96 threads executed simultaneously on a 12-core chip. The processor also makes use of very large amounts of on- and off-chip edram caches, and on-chip memory controllers to enable very high bandwidth to memory and system I/O. High performance computing integrator OCF provides installation, integration and support for the IBM POWER8 server. Whether you are modelling CFD in a commercial or academic organisation, fast reliable processing of your analyses is key. The OCF high speed platform delivers benefits across a wide range of disciplines, including aerospace, automotive, power generation, chemical manufacturing, medical research, and astrophysics. OCF combines the benefits of OpenFOAM which offers users complete freedom to customise and extend its existing functionality, with the high performance benefits of POWER8, for faster, more reliable modelling.

4 Benchmarks OpenFOAM on POWER8 is a true high performance computing solution for the solution and analysis of problems that involve fluid flows. A recent benchmark study showed that OpenFOAM on POWER8 was 3x faster than the x86 platform. For benchmarking, OpenFOAM was compiled on x86 and POWER8 (with only minor configuration changes) and two benchmarks were run. One used a motorbike example and the other used a car example, and the results illustrated a number of benefits. Motorbike Performance Running different problem sizes on P8, Ivybridge and Haswell Best threads/socket setting used for every data point Conclusion POWER8 is 1.5-3x faster than x86 due to: Memory Bandwidth: 3x Caches: 2x SMT Runtimes simplefoam Runtime (s) E+00 5.E+07 1E+08 Cells P8 x86 Ivybridge x86 Haswell Largest Case (100M Cells): Ivybridge seems to reach memory limit (96GB), although not swapping Similar but less obvious effect on P8 (128 GB) Haswell box has more memory (256GB) è linear behaviour Smaller Cases Show memory bandwidth dependence

5 Car Performance Conclusion Similar behaviour than motorbike Speedup x Larger advantage for P8 for larger cases simplefoam Runtime [s] x 9M 2.4x 40M P8 Ivybridge Dynamic Simulation pisofoam: Simulates transient behaviour Runtimes even longer than simplefoam hinders industrial use pisofoam Conclusion Similar speedup as simplefoam x 1.7x 2.2x P8 Ivybridge M 1000 steps 25M 300 steps 40M 300 steps The key benefits of OpenFOAM on Power are: Achieve up to 3x better performance Make huge productivity gains POWER8 allows GPU acceleration OpenFOAM scales well on POWER8 To view the benchmark details and results in full, please download the results here

6 In summary POWER8 offers up to 3x better performance than x86 on typical benchmarks OpenFOAM scales well on POWER8 GPU acceleration with POWER8 is possible OpenFOAM remains the application of choice for its reliability and openness, which offers users complete freedom to customise and extend its existing functionality, either by themselves or by others. Almost everything (including meshing, and pre- and post-processing) runs in parallel as standard, enabling users to take full advantage of computer hardware at their disposal. HPC experts OCF can install, customise and optimise for your application by combining OpenFOAM with POWER8 in order to deliver the right solution. You are invited to take a test drive in order to see for yourself what this powerful combination can offer: click here. OCF PLC 5 Rotunda Business Centre Thorncliffe Park Chapeltown Sheffield S35 2PG Tel: info@ocf.co.uk Website: Specialty Power Systems