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Vectorizing the Community Land Model

Oak Ridge National Laboratory Climate and Carbon Research Institute Oak Ridge, Tennessee 37831-6008, USA, forrest{at}climate.ornl.gov

Mariana Vertenstein

National Center for Atmospheric Research Boulder, CO, USA

Hideyuki Kitabata

Central Research Institute of Electric Power Industry, Japan

James B. White, III

Oak Ridge National Laboratory Climate and Carbon Research Institute Oak Ridge, Tennessee 37831-6008, USA

In this paper we describe our extensive efforts to rewrite the Community Land Model (CLM) so that it provides good vector performance on the Earth Simulator in Japan and the Cray X1 at Oak Ridge National Laboratory. We present the technical details of the old and new internal data structures, the required code reorganization, and the resulting performance improvements. We describe and compare the performance and scaling of the final CLM Version 3.0 (CLM3.0) on the IBM Power4, the Earth Simulator, and the Cray X1. At 64 processors, the performance of the model is similar on the IBM Power4, the Earth Simulator, and the Cray X1. However, the Cray X1 offers the best performance of all three platforms tested from 4 to 64 processors when OpenMP is used. Moreover, at low processor counts (16 or fewer), the model performs significantly better on the Cray X1 than on the other platforms. The vectorized version of CLM was publicly released by the National Center for Atmospheric Research as the standalone CLM3.0, as a part of the new Community Atmosphere Model Version 3.0 (CAM3.0), and as a component of the Community Climate System Model Version 3.0 (CCSM3.0) on June 23, 2004.

Key Words: Community Land Model • CLM • Community Climate System Model • CCSM • vectorization • Cray X1 • Earth Simulator

International Journal of High Performance Computing Applications, Vol. 19, No. 3, 247-260 (2005)
DOI: 10.1177/1094342005056113


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