Abstract: A method of preventing lockout and stalling conditions in a multi-node system having a plurality of nodes which includes initiating a processor request to a shared level of cache in a requesting node, performing a fabric coherency establishment sequence on the plurality of nodes, issuing a speculative memory fetch request to a memory, detecting a conflict on one of the plurality of nodes and communicating the conflict back to the requesting node within the system, canceling the speculative memory fetch request issued, and repeating the fabric coherency establishment sequence in the system until the point of conflict is resolved, without issuing another speculative memory fetch request. The subsequent memory fetch request is only issued after determining the state of line within the system, after the successful completion of the multi-node fabric coherency establishment sequence.

Abstract: The method includes initiating a processor request to a cache in a requesting node and broadcasting the processor request to remote nodes when the processor request encounters a local cache miss, performing a directory search of each remote cache to determine a state of a target line's address and an ownership slate of a specified address, returning the state of the target line to the requesting node and forming a combined response, and broadcasting the combined response to each remote node. During a fetch operation, when the directory search indicates an IM or a Target Memory node on a remote node, data is sourced from the respective remote cache and forwarded to the requesting node while protecting the data, and during a store operation, the data is sourced from the requesting node and protected while being forwarded to the IM or the Target Memory node after coherency has been established.

Abstract: A method and apparatus for eliminating, in a multi-nodes data handling system, contention for exclusivity of lines in cache memory through improved management of system buses, processor cross-invalidate stacks, and the system operations that can lead to these requested cache operations being rejected.

Abstract: Cache coherency latency is reduced through a method and apparatus that expedites the return of line exclusivity to a given processor in a multi-node data handling system through enhanced inter-node communications.

Abstract: A method of preventing lockout and stalling conditions in a multi-node system having a plurality of nodes which includes initiating a processor request to a shared level of cache in a requesting node, performing a fabric coherency establishment sequence on the plurality of nodes, issuing a speculative memory fetch request to a memory, detecting a conflict on one of the plurality of nodes and communicating the conflict back to the requesting node within the system, canceling the speculative memory fetch request issued, and repeating the fabric coherency establishment sequence in the system until the point of conflict is resolved, without issuing another speculative memory fetch request. The subsequent memory fetch request is only issued after determining the state of line within the system, after the successful completion of the multi-node fabric coherency establishment sequence.

Abstract: A method to use of dual valid bit sets including a regular bit set and alternate valid bits set which prevents new requests to a given cache line from entering a multi-nodal computer systems' nest system until all requests to the given cache line have been completed successfully. By providing the alternate valid bits the dual set of resource valids for each remote requester is provided for each remote requester, where one set of valids indicates if the resource is valid and actively working on the line, and the other set of valids indicates if the resource was valid but encountered some conflict that requires resolution before the request can complete. Only on successful reload and completion of the remote operation does this alternate address valid bit reset and open the way for any pending interface requests to proceed, so all outstanding requests currently loaded in a local resource within the nest system are able to complete before new interface requests are allowed into the system.

Abstract: A modification of rank priority arbitration for access to computer system resources through a shared pipeline that provides more equitable arbitration by allowing a higher ranked request access to the shared resource ahead of a lower ranked requester only one time. If multiple requests are active at the same time, the rank priority will first select the highest priority active request and grant it access to the resource. It will also set a ‘blocking latch’ to prevent that higher priority request from re-gaining access to the resource until the rest of the outstanding lower priority active requesters have had a chance to access the resource.

Abstract: Improved access to retained data useful to a system is accomplished by managing data flow through cache associated with the processor(s) of a multi-node system. A data management facility operable with the processors and memory array directs the flow of data from the processors to the memory array by determining the path along which data evicted from a level of cache close to one of the processors is to return to a main memory and directing evicted data to be stored, if possible, in a horizontally associated cache.

Abstract: A method to use of dual valid bit sets including a regular bit set and alternate valid bits set which prevents new requests to a given cache line from entering a multi-nodal computer systems' nest system until all requests to the given cache line have been completed successfully. By providing the alternate valid bits the dual set of resource valids for each remote requester is provided for each remote requester, where one set of valids indicates if the resource is valid and actively working on the line, and the other set of valids indicates if the resource was valid but encountered some conflict that requires resolution before the request can complete. Only on successful reload and completion of the remote operation does this alternate address valid bit reset and open the way for any pending interface requests to proceed, so all outstanding requests currently loaded in a local resource within the nest system are able to complete before new interface requests are allowed into the system.