Abstract: Topology mapping in a distributed processing system that includes a plurality of compute nodes, including: initiating a message passing operation; including in a message generated by the message passing operation, topological information for the sending task; mapping the topological information for the sending task; determining whether the sending task and the receiving task reside on the same topological unit; if the sending task and the receiving task reside on the same topological unit, using an optimal local network pattern for subsequent message passing operations between the sending task and the receiving task; otherwise, using a data communications network between the topological unit of the sending task and the topological unit of the receiving task for subsequent message passing operations between the sending task and the receiving task.