The MPI parallel version of FDS can be used with multiple meshes to significantly reduce PyroSim/FDS solution times.
Then use the cluster option as described below.
If the user wants to assign meshes manually to processes, select the None option for Optimize Processor Utilization. However, the current implementation of the Intel MPI library does not perform this operation as efficiently as earlier, so solution times may more than double the times obtained using the default behavior. MPI will be launched with options that attempt to mimic the earlier “round-robin” behavior. If you select Create Process for Each Mesh, PyroSim will create as many processes as meshes. The default option for Optimize Processor Utilization is Basic and the default option for Parallel Execution Settings is Limit Processes Based on Logical Processor Count. To try other MPI options that are available when the number of meshes is greater than the number of logical processors, click Preferences on the File menu. This will provide reasonable solution times. The mesh assignment can be seen in the MESH lines of the FDS input file. This is done in the order of the meshes, so if your model has 10 meshes and your computer has 4 logical processors, the meshes will be assigned as shown below. By default, PyroSim will start the same number of processes as logical processors and will assign multiple meshes to each process. However, if the number of meshes is greater than the number of logical processors then PyroSim performs additional steps. If the number of meshes is less than or equal to the number of logical processors, then a process is started for each mesh and the solution proceeds. How PyroSim Currently Runs MPIīy default, when the user clicks Run FDS Parallel in PyroSim, PyroSim compares the number of meshes with the number of logical processors. This post does contain useful information for users who want additional background on MPI or who want to manually assign specific meshes to processes. This issue was addressed in PyroSim 2020.3 so most users can use the default Run FDS Parallel option with satisfactory solution times. During that time period, if a model had more meshes than available processors and the user selected the default Run FDS Parallel option, the last processor would be assigned all excess meshes and solution times would be long. This post addressed a problem that occurred with in FDS and PyroSim for versions 2019.1 through 2020.2.
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