Sequent Computer Systems, Inc.

Robert T Joersz

Thomas D Lovett

Robert J Safranek

Bruce Michael Gilbert

A multiprocessor system that assures forward progress of local processor requests for data by preventing other nodes from accessing the data until the processor request is satisfied. In one aspect of the invention, the local processor requests data through a remote cache interconnect. The remote cache interconnect tells the local processor to retry its request for data at a later time, so that the remote cache interconnect has sufficient time to obtain the data from the system interconnect. When the remote cache interconnect receives the data from the system interconnect, a hold flag is set. Any requests from other nodes for the data are rejected while the hold flag is set. When the local processor issues a retry request, the data is delivered to the processor and the hold flag is cleared. Other nodes may then obtain control of the data.

Distributed shared memory system having a first node that prevents other

A method and apparatus for maintaining processor consistency in a multiprocessor computer such as a multinode computer system are disclosed. A processor proceeds with write operations before its previous write operations complete, while processor consistency is maintained. A write operation begins with a request by the processor to invalidate copies of the data stored in other nodes. This current invalidate request is queued while acknowledging to the processor that the request is complete even though it has not actually completed. The processor proceeds to complete the write operation by changing the data. It can then execute subsequent operations, including other write operations. The queued request, however, is not transmitted to other nodes in the computer until all previous invalidate requests by the processor are complete. This ensures that the current invalidate request will not pass a previous invalidate request. The invalidate requests are added and removed from a processor's outstanding invalidate list as they arise and are completed. An invalidate request is completed by notifying the nodes in a linked list related to the current invalidate request that data shared by the node is now invalid.

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Portland, OR, United States of America

Robert T Joersz