Changes between Version 22 and Version 23 of AdaptParallelization

Timestamp:

Feb 13, 2012, 4:59:12 PM (12 years ago)

Author:

lnerger

Comment:

--

AdaptParallelization

@@ -78 +78 @@
 This completes the adaptation of the parallelization. The compilation of the model has to be adjusted for the added files holding the routine `init_parallel_pdaf` and the module `mod_parallel`. One can test the extension by running the compiled model. It should run as without these changes, because `mod_parallel` defines by default that a single model task is executed (`n_modeltasks=1`). If `screen` is set to 1 in the call to init_parallel_pdaf, the standard output should include lines like
 {{{
- PDAF: Initializing communicators
+ Initialize communicators for assimilation with PDAF
 
                   PE configuration:
@@ -89 +89 @@
      3       3      1      3      4      0       T
 }}}
-These lines show the configuration of the communicators. This example was executed using 4 processes and `n_modeltasks=1`.
+These lines show the configuration of the communicators. This example was executed using 4 processes and `n_modeltasks=1`. (In this case, the variables `npes_filter` and `npes_model` will have a value of 4.)
 
 
-To test parallel model tasks one has to set the variable `n_modeltasks` to a value larger than one. Now, the model will execute parallel model tasks. This can result in the following effects:
+To test parallel model tasks one has to set the variable `n_modeltasks` to a value larger than one. Now, the model will execute parallel model tasks. For `n_modeltasks=4` and running on a total of 4 processes the output from init_parallel_pdaf will look like the following:
+{{{
+ Initialize communicators for assimilation with PDAF
+
+                  PE configuration:
+   world   filter     model        couple     filterPE
+   rank     rank   task   rank   task   rank    T/F
+  ----------------------------------------------------------
+     0       0      1      0      1      0       T
+     1              2      0      1      1       F
+     2              3      0      1      2       F
+     3              4      0      1      3       F
+
+}}}
+In this example only a single process will compute the filter analysis (`filterPE=.true.`). There are now 4 model tasks, each using a single process.
+
+Using multiple model tasks can result in the following effects:
  * The standard screen output of the model can by shown multiple times. This is due to the fact that often the process with `rank=0` performs screen output. By splitting the communicator `COMM_model`, there will be as many processes with rank 0 as there are model tasks. 
  * Each model task might write file output. This can lead to the case that several processes try to generate the same file or try to write into the same file. In the extreme case this can result in a program crash. For this reason, it might be useful to restrict the file output to a single model task. This can be implemented using the variable `task_id`, which is initialized by `init_parallel_pdaf` and holds the index of the model task ranging from 1 to `n_modeltasks`. (For the ensemble assimilation, it can be useful to switch off the regular file output of the model completely. As each model tasks holds only a single member of the ensemble, this output might not be useful. In this case,  the file output for the state estimate and perhaps all ensemble members should be done in the pre/poststep routine of the assimilation system.)
+
 
 '''Remark:''' For the compilation with a real MPI library, one has to ensure that the header file (`mpif.h`) of the MPI-library is used for both the model and PDAF. (Thus in the include file for make, one might have set `MPI_INC =`. The include directory `dummympi` specified in some of the include files, will not be compatible with all MPI implementations.