Multinode computer system with cache for combined tags

In a computer having a number of nodes at least one of which is a home node that includes a processor, local memory and a remote cache, a method of updating data stored in the local memory when valid data for the local memory is stored in a remote node, the method comprising the following steps:

• requesting the remote node to send a copy of the valid data to the home node;
• combining on the home node a cache tag of the remote cache including a cache state with a memory tag for a memory block containing the data being updated as portions of a combined tag, the combined tag tracking the states of the local memory and remote cache;
• storing on the home node the combined tag in a tag cache;
• modifying the combined tag to reflect current states of the local memory and remote cache;
• and
• once the valid data is received from the remote cache of the other node, storing the valid data in the local memory.

In a computer having a number of nodes at least one of which is a home node including a processor, local memory and a remote cache, an apparatus for updating data stored in the local memory when valid data for the local memory is stored in a remote cache of another node, comprising:

• storage for memory tags for each block of local memory, a memory tag including a memory state and a pointer;
• storage for cache tags for each cache line stored in the remote cache of the home node, the cache tags including a cache state;
• a protocol engine for combining a cache tag of the remote cache of the home node with a memory tag as portions of a combined tag;
• and
• a tag cache for storing the combined tags, a combined tag enabling the protocol engine to act as a cache controller for requesting the valid data from the other node and as a memory controller for responding to requests for the data while it is in the process of being obtained.

In a computer having a number of nodes at least one of which is a home node that includes a processor, local memory and a remote cache, a method of updating data stored in the local memory when valid data for the local memory is stored in another node, the method comprising the following steps:

• requesting the other node to send a copy of the valid data to the remote cache of the home node;
• once the valid data is received from the other node, storing the valid data in the local memory of the home node;
• and
• indicating that the valid data is stored in the local memory of the home node.