Scaling the SIESTA Magnetohydrodynamics Equilibrium Code

Abstract

We report the results of a scaling effort that increases both the speed and resolution of the SIESTA magnetohydrodynamic equilibrium code. SIESTA is capable of computing three-dimensional plasma equilibria with magnetic islands at high spatial resolutions for toroidally confined plasmas. Starting with a small-scale parallel im- plementation, we identified scale-dependent bottlenecks of the code and developed scalable alternatives for each performance-significant functionality, cumulatively increasing the runtime speed and scalability with the number of processors. The net outcome is an improvement in speed by over ten-fold, utilizing a few thousand processors, en- abling SIESTA to simulate high spatial-resolution scenarios in under an hour for the first time.