IPSL parallelisation

To run the OASIS3 executable on more than one process in IPSL parallelisation mode, OASIS3 must be compiled with the CPP key use_oasis_para (see 8.1.2).

With IPSL parallelisation mode, each OASIS3 process is totally independent of the others. Therefore, the user has to provide one separate configuration file per process and the different files must be named namcouple_x where x is the number of the corresponding OASIS3 process. Each OASIS3 process will receive, treat, and send the coupling fields described in its configuration file namcouple_x. Note that if OASIS3 was compiled with the CPP key use_oasis_para, the configuration file suffix is mandatory, even if OASIS3 runs in fact with only one process - in this case, the suffix is _0.

Although this parallelisation mode presents the advantage of removing the bottleneck that can appear when only one OASIS process receives and sends all the coupling fields, there are few constraints associated:

• As stated above, the configuration file namcouple has to be splitted into different namcouple_x, one per process. In one namcouple_x the total number of coupling fields treated by OASIS3 process x must be given on the line below the $NFIELDS keyword and only these coupling fields must be detailed.

  If the maximum number of prism_def_var_proto called by ANY component model in the coupled system is greater than twice the number of fields listed in the namcouple_x (which is often the case when OASIS3 is used in parallel mode), this maximum number of prism_def_var_proto has to be specified on the same line (below the $NFIELDS keyword) after the total number of fields exchanged (see also section 5.2).

• This mode is available only with the MPI1 CLIM communication technique (see 5.2).

• In this mode, the grid data files have to be created by the user before the run (see also 4.2).

• Binary restart files do not work with this mode; NetCDF files have to be used

• The different OASIS3 executables cannot share the same coupling restart file (see section 7.3). Therefore, the same coupling restart file cannot be indicated in different namcouple_x configuration files. The recommendation here is to use one separate coupling restart file per coupling field.