Multiprocessing system employing address switches to control mixed broadcast snooping and directory based coherency protocols transparent to active devices

A multiprocessing system comprising:

• a memory subsystem including a directory, the directory including a plurality of directory entries corresponding to memory locations mapped to said memory subsystem;
• a plurality of processing subsystems each including a cache for storing blocks corresponding to selected ones of said memory locations;
• a network interconnecting said plurality of processing subsystems and said memory subsystem;
• a mode unit configured to provide an indication of whether a given block is a point-to-point mode block or a broadcast mode block;
• wherein the network is configured to route a coherency request for said given block initiated by one of said processing subsystems to said directory in response to said indication indicating said given block is a point-to-point mode block, and wherein said network is configured to broadcast said coherency request to said memory subsystem and to each of said plurality of processing subsystems in response to said indication indicating said given block is a broadcast mode block, whereby a conveyance of said coherency request through said network according to either a directory protocol or a broadcast protocol is performed transparent to said one of said processing subsystems.

A method of operating a multiprocessing system including a plurality of processing subsystems and a memory subsystem interconnected through a network, the method comprising:

• a first processing subsystem initiating a coherency request;
• and
• a mode unit indicating whether said coherency request is to be transmitted through said network according to a directory protocol or a broadcast protocol;
• said network conveying said coherency request using either said directory protocol or said broadcast protocol according to said indication and transparent to said first processing subsystem.

A multiprocessing system comprising:

• a plurality of processing subsystems;
• a memory subsystem;
• a network interconnecting said plurality of processing subsystems and said memory subsystem;
• and
• a mode unit configured to control whether a coherency request is transmitted through said network according to a directory protocol or a broadcast protocol, whereby a conveyance of said coherency request through said network according to either said directory protocol or said broadcast protocol is performed transparent to said plurality of processing subsystems.