Patent ID: 8601237

Claim:
A method of performing a deterministic reduction operation in a parallel computer, the parallel computer comprising a plurality of compute nodes, each compute node comprising a plurality of computer processors and a Collectives Acceleration Unit (CAU), the CAU coupling computer processors of compute nodes to one another for data communications in a cluster data communications network, the method comprising: organizing a particular plurality of processors of a particular plurality of compute nodes of the parallel computer and a root CAU into a branched tree topology, wherein the root CAU comprises a root of the branched tree topology and the particular plurality of processors comprise children of the root CAU; receiving, by the root CAU from each of the processors in the particular plurality of processors of the branched tree topology, in any order, dummy contribution data, wherein each processor of the particular plurality of processors is restricted from sending any other data to the root CAU prior to receiving an acknowledgement of receipt from the root CAU; sending, by the root CAU to the processors in the branched tree topology, in a predefined order, acknowledgements of receipt of the dummy contribution data; providing, by each processor in the branched tree topology, contribution data to the root CAU only after receiving an acknowledgement; receiving, by the root CAU from the processors in the branched tree topology in the predefined order, the contribution data to the reduction operation; and reducing, by the root CAU, the received contribution data.