If you are using any of the parallel operating environments already supported by LoadLeveler, you do not have to use the parallel API. However, if you have another application environment that you want to use, you need to use the subroutines described here to interface with LoadLeveler.
The parallel job API consists of two subroutines. ll_get_hostlist acquires the list of LoadLeveler selected parallel nodes, and ll_start_host starts the parallel task under the LoadLeveler starter.
The following section describes how parallel job submission works. Understanding this will help you to better understand the parallel API.