Multiprocessor system with shared memory using mixed broadcast snoops and directory-based coherence protocols

摘要

A multiprocessor computer system is configured to selectively transmit address transactions using either a broadcast mode or a point-to-point mode. Depending on the mode of transmission selected, either a directory-based coherency protocol or a broadcast snooping coherency protocol is implemented to maintain coherency within the system. A computing node is formed by a group of clients which share a common address and data network. The address network is configured to determine whether a particular transaction is to be conveyed in broadcast mode or point-to-point mode. In one embodiment, the address network includes a mode table with entries which are configurable to indicate transmission modes corresponding to different regions of the address space within the node. Upon receiving a coherence request transaction, the address network may then access the table in order to determine the transmission mode, broadcast or point-to-point, which corresponds to the received transaction. In a further embodiment, network congestion may be monitored and transmission modes adjusted accordingly. For example, when network utilization is high, the number of transactions which are broadcast may be reduced. Alternatively, when network utilization is low, the number of broadcasts may be increased to take advantage of available bandwidth. IMAGE