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Performance Breakdowns on higher Core Numbers

In case you would like to optimize the performance of your application or you observe performance breakdowns on higher core numbers please test the following scenario:

The variable PSP_ONDEMAND influences the creation of MPI connections. If you change the value of this variable into PSP_ONDEMAND=1 within your batch script, then the connections will be created dynamically when they are used the first time. We observed a performance increase of several applications with these dynamic connections.
Our recommendation is to perform a test run with PSP_ONDEMAND=1 and to compare the results to the runs without this specification.

Attention: If you have all-to-all communication in your application, PSP_ONDEMAND=1 might not be possible, see Using dynamic memory allocation for MPI connections.


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