Extending cache coherency protocols to support locally buffered data

An apparatus comprising:

• execution resources to execute a transactional store operation within a transaction referencing an address associated with a data item, wherein the transaction includes a grouping of instructions, operations or micro-operations to be executed as an atomic group;
• and
• a cache memory coupled to the execution resources to hold the data item in a buffered coherency state in response to the execution resources executing the transactional store operation;
• and
• control logic associated with the cache memory to transition a cache line from being associated with the buffered coherency state to a modified coherency state responsive to the transaction being committed, wherein the cache line to be associated with the buffered coherency state comprises a state entry associated with the cache line holding a buffered state value to indicate the cache line is held in the buffered coherency state.

An apparatus comprising:

• a cache memory to hold at least a portion of a data item in a cache line to be associated with a buffered coherency state in response to the data item being transactionally accessed within a transaction;
• and
• control logic associated with the cache memory to transition the cache line from being associated with the buffered coherency state to a modified coherency state in response to the transaction being committed, wherein:
• the cache line to be associated with a buffered coherency state comprises a coherency entry associated with the cache line to hold a buffered coherency value;
• and
• the control logic to transition the cache line from being associated with the buffered coherency state to a modified coherency state comprises updating the coherency entry from holding the buffered coherency value to hold a modified coherency state.

A method comprising:

• encountering a transactional store referencing an address associated with a data item, wherein the transactional store is a part of a transaction that includes a grouping of instructions, operations or micro-operations to be executed as an atomic group;
• performing a buffered store of the data item to associate the data item with a buffered state in response to encountering the transactional store by performing a buffered store of at least a portion of the data item to a cache line in a cache memory associated with the address associated with the data item and updating a coherency state entry corresponding to the cache line to a buffered state value to associate at least the portion of the data item held in the cache line with the buffered state;
• and
• in response to the data item being associated with the buffered state, providing a hit response to a local access to the data item and providing a miss response to an external access to the data item and updating the coherency state entry to an invalid state value to associate at least the portion of the data item held in the cache line with an invalid state in response to the data item being associated with the buffered state and providing a miss response to the external access to the data item.