Technique for managing a cache memory in a system employing transactional memory including storing a backup copy of initial data for quick recovery from a transaction abort

摘要

A technique is described for managing a cache structure in a system employing transactional memory. The apparatus comprises processing circuitry to perform data processing operations in response to instructions, the processing circuitry comprising transactional memory support circuitry to support execution of a transaction, and a cache structure comprising a plurality of cache entries for storing data for access by the processing circuitry. Each cache entry has associated therewith an allocation tag, and allocation tag control circuitry is provided to control use of a plurality of allocation tags and to maintain an indication of a current state of each of those allocation tags. The transactional memory support circuitry is arranged, when initial data in a chosen cache entry is to be written to during the transaction, to cause a backup copy of the initial data to be stored in a further cache entry and to cause the allocation tag control circuitry to associate with that further cache entry a selected allocation tag selected for the transaction. The current state of that selected allocation tag is updated to a first state which prevents the processing circuitry from accessing that further cache entry. In the event that the transaction is aborted prior to reaching a transaction end point, the transactional memory support circuitry causes the chosen cache entry to be invalidated, and the allocation tag control circuitry changes the state of the selected allocation tag to a second state that allows the processing circuitry to access the further cache entry. As a result, this enables a hit to subsequently be detected within the cache structure for the initial data without a requirement to refetch the initial data into the cache structure. This can give rise to significant performance enhancements.