Method for increasing efficiency in a multi-processor system and multi-processor system with increased efficiency

Abstract

The multi-processor system according to the present invention includes at least two processors, a system bus providing communication between the responses to commands on the system bus. One of the processors generates a snoop response to a command, associated with the same real address as the snooped command, which issued from the processor. In response to a command requesting invalidation of a cache line, a cache within the processor conditionally casts back the cache line to a transition cache in the processor. Based on the system response to the invalidation command, the transition cache either discards the cast back or converts the cast back into a command for writing the cache line in the main memory of the system. The processor also converts an exclusive read command requiring a reservation to a non-exclusive read command if that reservation has been lost prior to placing the command on the system bus. Furthermore, the transition cache in the processor may shift the memory coherency image state for a non-exclusive command, which is waiting for data to return, if a command associated with the same real address is snooped. In response to a command requesting a cache line, the cache in the processor copies that cache line to the transition cache and updates the state for the cache line. The transition cache holds the cache line until a system response is received.