Method and Apparatus for Active Software Disown of Cache Line's Exlusive Rights

A computer system, comprising:

• a computer system having a storage controller and a processing unit coupled to cache memory involving various ownership states as to a cache line, which states include a read-only or shared state and an exclusive state for holding the line exclusive for software modification by hardware during the time that the line is in said exclusive state, and interface controls for allowing software running on said computer system to indicate to the hardware of the processing unit that its storage modification of a particular cache line in the exclusive state is done, and will not be doing any modification for the time being,
• said interface controls having an interface receiving mechanism for communicating with said storage controller a software indication that its storage modification of said particular cache line is done and that any modification will not be done for the time being, said interface controls preventing a premature launch of a demote request,
• and executing said a demote request with regard to said particular cache line indicated by said software in said processing unit to cause the processing unit to actively relinquish control of its exclusive ownership of said particular cache line and preemptively updating the ownership status in the storage controller of said particular cache line to a read-only or shared state.

A computer system comprising one or more microprocessor cores each having an instruction dispatch unit, a fixed point unit and a load store,

• and a cache subsystem, and wherein demote requests are performed by the cache subsystem and the processor cores execute a demote instruction as a one cycle superscalar instruction that performs no architectural updates.

A computer system comprising:

• a storage controller, a plurality of processors forming a processing unit and a cache subsystem, and a cache interface establishing a direct connection between a processor and a storage controller upon receipt of a demote request issued by a processor of the processing units.

A method of managing storage updates in a computer system, comprising:

• providing via software input an indication that a particular cache line is no longer required for any further storage update by a processor owning said particular cache line for store access, and
• treating said indication that a particular cache line is no longer required for any further storage update as an indication that the processor is at the end of its last storage updating and can be demoted from its storage access status to be next used by any of various processes that are running of said computer system.