Building OpenIFS

Build configuration

Before compiling the OpenIFS model, the build configuration must first be set by several environment variables:

OIFS_ARCH  - This sets the architecture of the computer. By default, the FCM build configuration assumes x86_64 (i.e. Linux).

OIFS_COMP - This sets the choice of compiler. The default is 'gnu' which means the gfortran/gcc compilers will be used.

OIFS_BUILD - This sets the type of build.

These environment variables directly correspond to the names of the FCM configuration files in the oifs/make/fcmcfg/ directory in the OpenIFS source. Please see this directory for the choices provided.

Build types: OIFS_BUILD sets the type of build and there will be one FCM configuration file for each type. Build types provided are:

• opt - Recommended optimized compile settings for OpenIFS for this compiler. Tested to provide best performance for this platform & compiler.
• noopt - Debugging options. No optimization set for all of the OpenIFS code. Suitable for use with a debugger.
• nansC - Debugging options with extra checks. Array bound checking enabled and variables initialized to NAN (not-a-number). Use of a variable set to NAN will trigger a floating point exception. This option is useful for debugging purposes but will run the slowest.

e.g.

export OIFS_ARCH=x86_64
export OIFS_COMP=intel
export OIFS_BUILD=opt

means using the Intel ifort compiler on a x86_64 computer architecture and the model will be compiled with full optimization compiler settings. Also the FCM build system will expect to find a file:

make/fcmcfg/x86_64-intel-opt.cfg

Setting:

export OIFS_ARCH=aix_pwr6
export OIFS_COMP=xlf
export OIFS_BUILD=noopt

means FCM will look for a file:

make/fcmcfg/aix_pwr6-xlf-noopt.cfg

suitable for building on IBM Power6 architecture using the XLF/XLCC compilers using non-optimized settings.

Building for other systems/environments

As the environment variables refer to the corresponding filename in the make/fcmcfg  directory it is straightforward to create a build configuration for other environments. Take a copy of an existing file and modify it as necessary. It's also possible to alter compile options by the use of additional environment variables (see below). Which approach you use depends on your personal preference. Be aware however that the optimization compiler flags in the provided configuration files are the recommended ones. It is impossible to test all combinations of compiler flags so OpenIFS may become unstable or performance may reduce if higher optimizations are tried.

Setting the location of libraries

OpenIFS requires a number of libraries (see Prerequisites) to compile. As well as the GRIB_API library, the LAPACK & BLAS numerical libraries are required. An MPI library is also required but this is assumed to be provided by compiler wrappers provided by the MPI implementation (e.g. the command mpif90 rather than gfortran).

To set the location of the GRIB_API & LAPACK libraries, two other environment variables need to be defined as the defaults in the FCM configuration files will most likely not be appropriate (or you can choose to edit the FCM configuration files in make/fcmcfg).

OIFS_GRIB_API_DIR - Defines the location of the grib_api library. If you followed the example in 'Installing grib_api for OpenIFS' it will be installed in $HOME/ecmwf/grib_api_gcc.

OIFS_LAPACK_LIB - Defines the location of the directory containing the liblapack.a and libblas.a files. This varies from system to system but typically /usr/local/lib.

e.g.

export OIFS_GRIB_API_DIR=$HOME/ecmwf/grib_api_gcc
export OIFS_LAPACK_LIB="-L/usr/local/lib -llapack -lblas"

Compiling OpenIFS

Once the environment variables are set, OpenIFS can be compiled (make sure you have edited your PATH environment variable to add the FCM installation /bin directory). Assuming you are in the directory where the OpenIFS source code was unpacked:

cd make
fcm make -f fcmcfg/oifs.cfg

The command 'fcm make' starts the compilation. The -f option specifies the location of the master configuration file for OpenIFS. For more information is available on the available fcm command options.

This generates output similar to:

[init] make                # 2012-12-20 19:59:59Z
[init] make config-parse   # 2012-12-20 19:59:59Z
[info] config-file=...../make/fcmcfg/oifs.cfg
[info] config-file= - ...../make/fcmcfg/x86_64-gnu-opt.cfg
[done] make config-parse   # 0.3s
[init] make dest-init      # 2012-12-20 19:59:59Z
[info] mode=new
[done] make dest-init      # 0.3s
[init] make build          # 2012-12-20 20:00:00Z
[info] sources: total=2194, analysed=2194, elapsed-time=11.7s, total-time=32.2s
[info] target-tree-analysis: elapsed-time=9.8s
[info] compile   targets: modified=2073, unchanged=0, total-time=1095.5s
[info] compile+  targets: modified=628, unchanged=0, total-time=1.6s
[info] ext-iface targets: modified=1247, unchanged=0, total-time=21.9s
[info] install   targets: modified=120, unchanged=0, total-time=0.3s
[info] link      targets: modified=1, unchanged=0, total-time=18.3s
[info] TOTAL     targets: modified=4069, unchanged=0, elapsed-time=316.3s
[done] make build          # 329.1s
[done] make                # 329.8s

Verbose compilation

The default output of FCM is quite terse. To get more verbose output use the '-v' option. Also if you have a multicore machine you can use the -j option to specify additional processes to build in parallel.

e.g.

fcm make -v -j 4 -f fcmcfg/oifs.cfg

will produce a more detailed report and use 4 processes to analyse and build the model code in parallel.

Successful compilation

After a successful compilation, the OpenIFS executable, master.exe, can be found in the 'make/build' subdirectory:

% ls
build  fcmcfg
% ls build
bin   include   o
% ls build/bin
master.exe

The 'build' subdirectory is generated by FCM. The build/include directory contains all the files referenced in the code by a '#include' statement. This includes the Fortran interface block files which are auto-generated by FCM and end in .intfb.h. The build/o directory contains all the compiled object files. The OpenIFS build does not place any additional files in the src directory (known as building 'out of source').

Compilation problems

If you get the message:

fcm make -f fcmcfg/oifs.cfg
/bin/ksh: fcm: not found [No such file or directory]

you need to add the 'bin' directory of the unpacked FCM installation to your PATH environment variable:

export PATH=$PATH:$HOME/fcm-2-3/bin