Patent ID: 8140826

Claim:
A method for executing a gather operation on a parallel computer, the parallel computer comprising a plurality of compute nodes, the compute nodes organized into at least one operational group of compute nodes for collective parallel operations of the parallel computer, each compute node in the operational group assigned a unique rank, and one compute node assigned to be a logical root, the method comprising: receiving, by each compute node, a control message indicating a beginning of the gather operation; initializing, by each compute node, a position counter; configuring, by the logical root, a result buffer for the logical root, the result buffer having positions, each position corresponding to a ranked node in the operational group and for storing contribution data gathered from that ranked node; repeatedly for each position in the result buffer: determining, by each compute node of the operational group, whether a current position in the result buffer corresponds with the rank of the compute node, including: determining whether a current value of the position counter matches the rank of the compute node, identifying that the position in the result buffer corresponds with the rank of the compute node if the current value of the position counter matches the rank of the compute node, and identifying that the position in the result buffer does not correspond with the rank of the compute node if the current value of the position counter does not match the rank of the compute node, and incrementing the current value of the position counter; if the current position in the result buffer corresponds with the rank of the compute node, contributing, by that compute node, the compute node's contribution data, if the current position in the result buffer does not correspond with the rank of the compute node, contributing, by that compute node, a value of zero for the contribution data, and storing, by the logical root in the current position in the result buffer, results of a bitwise OR operation of all the contribution data by all compute nodes of the operational group for the current position, the results received through the global combining network.