Multiprocessor cache coherence system and method in which processor nodes and input/output nodes are equal participants

A computer system, comprising:

• an interconnect;
• a plurality of processor nodes, coupled to the interconnect, each processor node including:
• at least one processor core, each processor core having an associated memory cache for caching memory lines of information;
• an interface to a local memory subsystem, the local memory subsystem storing a multiplicity of memory lines of information;
• and
• a protocol engine implementing a predefined cache coherence protocol;
• wherein the local memory subsystem is embodied upon a single chip, along with the processor core, the memory cache, the interface and the protocol engine;
• and the computer system further comprises:
• a plurality of input/output nodes, coupled to the interconnect, each input/output node including:
• no processor cores;
• an input/output interface for interfacing to an input/output bus or input/output device;
• a memory cache for caching memory lines of information;
• an interface to a local memory subsystem, the local memory subsystem storing a multiplicity of memory lines of information;
• and
• a protocol engine implementing the predefined cache coherence protocol;
• wherein the local memory subsystem is embodied upon another single chip, along with the input/output interface, the memory cache, the interface and the protocol engine;
• wherein the protocol engine of each of the processor nodes and the protocol engine of each of the input/output nodes includes logic for sending an initial invalidation request to no more than a first predefined number of the processor nodes and input/output nodes associated with set bits in an identification field of a directory entry associated with a requested memory line of information;
• and
• wherein the processor nodes and the input/output nodes collectively comprise a plurality of system nodes, each of which includes:
• input logic for receiving a first invalidation request, the invalidation request identifying a memory line of information and including a pattern of bits for identifying a subset of the plurality of system nodes that potentially store cached copies of the identified memory line;
• and
• processing circuitry, responsive to receipt of the first invalidation request, for determining a next node identified by the pattern of bits in the invalidation request and for sending to the next node, if any, a second invalidation request corresponding to the first invalidation request, and for invalidating a cached copy of the identified memory line, if any, in the particular node of the computer system.