Method and apparatus for directory-based coherence with distributed directory management

摘要

A system for cache coherency comprises a memory. The memory comprises a plurality of data items and a plurality of directory information items, each data item uniquely associated with one of the plurality of directory information items. Each of the plurality of data items is configured in accordance with one of a plurality of access modes. Each of the plurality of directory information items comprises indicia of the access mode of its associated data item. A multiplexer couples to the memory and comprises a multiplex ratio. A plurality of buffers couple to the multiplexer and to the memory. The multiplex ratio is a function of the number of buffers in the plurality of buffers. A plurality of multiplexer/demultiplexers (MDMs) each uniquely couple to a different one of the plurality of buffers. A plurality of processing elements couple to the memory; each of the processing elements uniquely couples in a point-to-point connection to a different one of the plurality of MDMs. Each of the processing elements is configured to transmit a data request to its associated MDM, the data request identifying one of the plurality of data items and an access mode. The memory is configured to transmit a data response to each of the processing elements in response to a data request, the data response comprising the identified data item and its associated directory information. Each of the processing elements is further configured to receive the data response and to compare the associated directory information with the access mode of the data request and in the event that the associated directory information and the access mode of the data request are not compatible, to initiate coherence actions for the requested data item. A method for cache coherency is also provided.