Multiprocessor computer system employing a mechanism for routing communication traffic through a cluster node having a slice of memory directed for pass through transactions

Abstract

A multiprocessing computer system includes a plurality of nodes interconnected through a global interconnect network which supports cluster communications. An initiating node may launch a request to a remote node's memory. A remote cluster node may be reached by passing the request through one or more intermediate nodes configured in pass-through mode. Accordingly, various global network topologies may be supported. The pass-through mode may be advantageously accommodated using a node having hardware which is similar to other nodes in the system. More particularly, the pass through mechanism may be implemented without significantly altering a node's local bus transactions. In one specific implementation, when the system interface of a particular node receives a transaction, the address of the transaction is checked to determine if the transaction should be treated as a pass through transaction. Transactions of selected address regions may be specified as being pass through transactions during system initialization. When a transaction is identified as a pass through transaction, the system interface initiates a corresponding transaction on the local bus of the interface, with an indication that this transaction is a pass through transaction. The same interface or another interface may responsively reconvey the transaction upon another channel of the global network to thereby convey the transaction to its destination. In one embodiment, a pass through transaction is indicated on the local bus by clearing an MSB of the address for the transaction. In other respects, the transaction conveyed on the local bus is similar to other local bus transactions. Other unused fields of the local bus during the transaction may alternatively be used to indicate a pass through operation. Accordingly, the hardware of the node need not be significantly modified to support the pass through operations. Error messages from a remote node may be further conveyed through the pass through node to the initiating node.