Fregrid_gpu - NOAA-GFDL/FRE-NCtools GitHub Wiki

Introduction

Fregrid_gpu a grid tool available as part of FRE-NCTools. It is used to remap data from an input grid to an output grid with offloading capabilities to GPUs via OpenACC implementation. Fregrid_gpu is in development and currently supports the conservative remapping methods.

Fregrid_gpu algorithm overview

The main program is defined in fregrid_gpu.c and is very similar to the original fregrid program. For a typical fregrid_gpu usage, users need to provide the following command line arguments: interp_method; input mosaic file; output mosaic file or nlon and nlat for on-the-fly output grid generation; input data files containing the data to be remapped; name of the output file that will be generated; scalar fields to remap; and the name of the remap file to be generated or read in. Fregrid_gpu first parses these arguments, sets the a appropriate program flags, and allocates the necessary arrays and structs. Next, mosaic and grid files are read in or computed on-the-fly for latxlon output grid. Input field metadata is also read in and from this metadata, output field metadata is set. Setup_conserve_interp_gpu is then called to compute the exchange grid and populate the Interp struct where Interp contains the exchange grid information. Afterwards, for each vertical level for each variable and for each timepoint, do_scalar_conserve_interp_gpu is called where Interp is used to remap the data on the input grid to the output grid.

This Wiki details key conservative remapping concepts and algorithms in fregrid_gpu, and is organized into the following sections:

• Exchange grid
• Setup conserve interp gpu
• Creating the exchange grid gpu
• Do scalar conserve interp gpu