Multiprocessing system using an access to a second memory space to initiate software controlled data prefetch into a first address space

Abstract

A computer system defines a write transaction having a certain encoding as a prefetch command. A computer program developed for the computer system may include prefetch commands at points where the program has determined that a previously unreferenced coherency unit may be needed presently. By initiating the coherency activities for retrieving the coherency unit via a prefetch command, at least a portion of the latency inherent in that coherency activity may be experienced prior to executing an memory operation which accesses the coherency unit. In one embodiment, two prefetch commands are defined: a prefetch-shared command and a prefetch-modified command. The prefetch-shared command prefetches the coherency unit into the shared coherency state within the processing node which executes the prefetch command. On the other hand, the prefetch-modified command prefetches the coherency unit into the modified coherency state within the processing node which executes the prefetch command. When data from the coherency unit is received in the processing node, the data is transmitted across a local bus within the processing node to a memory. The data is stored into the local memory, thereby becoming available locally. The latency associated with the subsequent memory operation which accesses the coherency unit may thereby be decreased.

Dependencies are inferred from the claim text.