Performing optimized collective operations in an irregular subcommunicator of compute nodes in a parallel computer

An apparatus for performing optimized collective operations in an irregular subcommunicator of compute nodes in a parallel computer, the apparatus comprising a computer processor, a computer memory operatively coupled to the computer processor, the computer memory having disposed within it computer program instructions that, when executed, cause the apparatus to carry out the steps of:

• identifying, within the irregular subcommunicator, regular neighborhoods of compute nodes, wherein identifying regular neighborhoods of compute nodes comprises:
• establishing, by each respective compute node of the irregular subcommunicator, at least one logical plane that includes the respective compute node, wherein establishing the at least one logical plane comprises:
• identifying, in a positive direction of a first dimension, each logical plane that includes the respective compute node, a first compute node of the irregular subcommunicator that is one or more hops away from the respective compute node in a positive direction of a second dimension, wherein the second dimension is orthogonal to the first dimension;
• identifying, in a negative direction of the first dimension, each logical plane that includes the respective compute node and a second compute node of the irregular subcommunicator that is one or more hops away from the respective compute node in the positive direction of the second dimension;
• selecting, for each neighborhood from the compute nodes of the neighborhood, a local root node;
• assigning each local root node to a node of a neighborhood-wide tree topology;
• mapping, for each neighborhood, the compute nodes of the neighborhood to a local tree topology having, at its root, the local root node of the neighborhood;
• and
• performing a one way, rooted collective operation within the subcommunicator including:
• performing, in one phase, the collective operation within each neighborhood and performing in another phase, the collective operation amongst the local root nodes.

A computer program product for performing optimized collective operations in an irregular subcommunicator of compute nodes in a parallel computer, the computer program product disposed upon a computer readable medium, the computer program product comprising computer program instructions that, when executed, cause a computer to carry out the steps of:

• identifying, within the irregular subcommunicator, regular neighborhoods of compute nodes, wherein identifying regular neighborhoods of compute nodes comprises:
• establishing, by each respective compute node of the irregular subcommunicator, at least one logical plane that includes the respective compute node, wherein establishing the at least one logical plane comprises:
• identifying, in a positive direction of a first dimension, each logical plane that includes the respective compute node, a first compute node of the irregular subcommunicator that is one or more hops away from the respective compute node in a positive direction of a second dimension, wherein the second dimension is orthogonal to the first dimension;
• identifying, in a negative direction of the first dimension, each logical plane that includes the respective compute node and a second compute node of the irregular subcommunicator that is one or more hops away from the respective compute node in the positive direction of the second dimension;
• selecting, for each neighborhood from the compute nodes of the neighborhood, a local root node;
• assigning each local root node to a node of a neighborhood-wide tree topology;
• mapping, for each neighborhood, the compute nodes of the neighborhood to a local tree topology having, at its root, the local root node of the neighborhood;
• and
• performing a one way, rooted collective operation within the subcommunicator including:
• performing, in one phase, the collective operation within each neighborhood and performing in another phase, the collective operation amongst the local root nodes.