IBM Power Systems 775 Manual

Contents

Chapter 2. Application integration 131Figure 2-11 shows an example of a tree which interconnects eight processors (P0 - P7) byusing seven CAUs (C0 - C6), which results in each CAU with three neighbors (C3 includesonly two). This configuration is a binary tree because no CAU has more than three neighbors.Figure 2-11 CAU example tree 3Figure 2-12 shows an example of a tree which interconnects eight processors (P0a - P0g, P1)where the first seven processors are on the same node but are associated with differentpartitions. The eighth processor (P1) is on a different node. All processors use CAU C0, butthey are organized into two separate indexes (a and b). This type of tree structure in whichone tree features segments at multiple indexes of the same CAU, is useful when a treeincludes many neighbors that are different partitions within the same node.Figure 2-12 CAU Example Tree 4For optimal performance, CAUs that have one or more processors for a neighbor often resideon the same node as one of the processors. CAUs that do not have any processors as aneighbor (such as C1, C3, and C5, as shown in Figure 2-11), are on any node, including anode that does not have a processor that is part of the tree.Processors send CAU packets by putting them on the Send FIFO of an HFI. Processorsreceive CAU packets by pulling them from a Receive FIFO of an HFI. CAUs send and receiveCAU packets via an interface to both HFIs on the same node. Figure 2-13 on page 132 showsthe physical connections of the CAUs and processors to the HFIs and the Cluster Network. InImportant: In the example trees that are shown in the previous figures, there are moreprocessors than CAUs. Because of this condition, it is possible to define a skinny tree inwhich multiple CAUs have only two neighbors. This configuration results in more CAUsthan processors.Key:Cn = CAU on node “n”P0 P1 P2 P3 P4 P5 P6 P7C0Pn = processor on node“n”line = neighbors..C4C2 C6C1 C5C3Key:Cni= “i” th index of CAU on node nP0a P1C0aPnm = “m” processor on node “n”line = neighbors..C0bP0b P0c P0d P0e P0f P0g