Changes between Version 27 and Version 28 of AdaptParallelization


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Timestamp:
Dec 11, 2019, 4:08:25 PM (5 years ago)
Author:
lnerger
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  • AdaptParallelization

    v27 v28  
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    3434The parallel region of an MPI parallel program is initialized by calling `MPI_init`.  By calling `MPI_init`, the communicator `MPI_COMM_WORLD` is initialized. This communicator is pre-defined by MPI to contain all processes of the MPI-parallel program. Often it is sufficient to conduct all parallel communication using only `MPI_COMM_WORLD`. Thus, numerical models often use only this communicator to control all communication. However, as `MPI_COMM_WORLD` contains all processes of the program, this approach will not allow for parallel model tasks. In order to allow parallel model tasks, it is required to replace `MPI_COMM_WORLD` by an alternative communicator that is split for the model tasks. We will denote this communicator `COMM_model`. If a model code already uses a communicator distinct from `MPI_COMM_WORLD`, it should be possible to use that communicator.
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     36[[Image(//pics/communicators_PDAFonline.png)]]
     37[[BR]]'''Figure 1:''' Example of a typical configuration of the communicators using a parallelized model. In this example we have 12 processes over all, which are distributed over 3 model tasks (COMM_model) so that 3 model states can be integrated at the same time. COMM_couple combines each set of 3 communicators of the different model tasks. The filter is executed using COMM_filter which uses the same processes of the first model tasks (COMM_model 1).
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    3639== Using COMM_model ==