This poster outlines the speed increase in the inversion part of the BGS global modelling software after rewriting some of it in the SAC language

Bainbridge, Brian

Hamilton, Brian

Scholz, Sven-Bodo

Viessmann, Hans-Nikolai

NERC Open Research Archive

Improving Performance of the BGSGeomagnetic Field Modelling CodeH.-N. Viessmann, B. Bainbridge, B. Hamilton,S.-B. Scholz, S. M. Flowerhv15@hw.ac.uk, bba@bgs.ac.uk, bham@bgs.ac.uk, S.Scholz@hw.ac.uk, smf@bgs.ac.ukWhat is the BGS geomagnetic field modelling code?The BGS Geomagnetic Field Modelling code is used to develop mathematical models of theEarth’s magnetic field for scientific, government, and industry stakeholders. The models areconstructed from data collected from geomagnetic observatories around the globe and satellites inorbit (such as the ESA Swarm project shown on the left). Example models are the InternationalGeomagnetic Reference Field (IGRF), the World Magnetic Model (WMM), and the BGS GlobalGeomagnetic Model (BGGM). These models are derived from parent models output by theBGS code which generally have millions of input data to estimate thousands of coefficientsthat describe the Earth’s magnetic field. The scale of the task requires efficient parallelisedalgorithms in order to calculate these values in a reasonable amount of time and with consistentresults.ESA Swarm satellitesExamples of models produced by the codeIGRF a standard mathematical description of the Earth’s main magnetic field that is used widelyin studies of the Earth’s deep interior, its crust and its ionosphere and magnetosphere.WMM aims to provide a reliable estimate of the magnetic field’s strength and direction on ornear the Earth’s surface. It is used by many corporate and governmental organisations astheir standard model for navigation and in attitude and heading referencing systems. Manyelectronic devices, such as smartphones, incorporate the model to improve compress-basednavigation.BGGM widely used in the oil industry for directional drilling with Measurement-While-Drilling(MWD) magnetic survey tools. These tools measure the direction of the well-bore relativeto the direction of the local geomagnetic field and are used to navigate wells towardsprecisely known underground targets. An example of the model is shown on the right,which shows the angle between True North (towards the geographic North Pole) andhorizontal direction of the Earth’s magnetic field.Declination map of the globeThe ChallengeThe BGS modelling code is run on part of a 28× 16-core node, InfiniBand®-connected cluster. It is an MPI-based hand-parallelised code. Whilemost of the application code scales well, the code contains a bottleneck which is executed on a single node. This bottleneck inverts a matrix ofroughly 7000× 7000 elements by iteratively computing its eigenvectors.The goal is to leverage compiler technology from Heriot-Watt University to enable scaling of this bottleneck code.Our SolutionWe use the SaC programming language and compiler ecosystem to rewrite the bottleneck code,and subsequently auto-parallelise it. We re-implement 200 lines of Fortran code in SaC. Whilemost of that code can be rewritten in a straight-forward manner, 30 lines of the code wereactually re-factored. This re-factoring addressed two aspects: Firstly, the SaC code, in contrastto the original Fortran code, reflects the two-dimensional nature of the algorithm more directly.Secondly, this two-dimensional formulation reveals the data-parallelism present in the algorithm(the data can be segmented into separate computable chunks). This enables our compiler toutilise all the cores on the executing node.SaC is freely available fromhttp://www.sac-home.org/.ResultsWe run the modified code on the originaldata using a single 16-core node of the clustercontaining two Intel® Xeon® CPUs E526502.6GHz with 128 GB RAM. For the Fortranruntimes of the original code we use the PGIcompiler pgfortran 14.7-0. For the SaC run-times we use the SaC compiler sac2c v.1.0 rev18494 as frontend and gcc 4.8.2 as backendcompiler.1 2 4 8 1612243648 •483220131012# of Threads used by SaC codeTime(minutes)Runtime Comparison — Fortran vs. SaCFortran RuntimeSaC Runtimes

Improving performance of the BGS Geomagnetic Field Modelling Code

http://nora.nerc.ac.uk/513988/1/ViessmannEtAl2015_SAC-globmod.pdf

Improving performance of the BGS Geomagnetic Field Modelling Code

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