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

• US 7,222,220 B2
• Filed: 06/23/2003
• Issued: 05/22/2007
• Est. Priority Date: 05/01/2001
• Status: Expired due to Term

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Cypher, Robert E., Singhal, Ashok
• Primary Examiner(s): Peugh; Brian
• Assistant Examiner(s): DILLER, JESSE DAVID
• Application Number:
  US10/601,402
• Publication Number:
  US 20040002992A1
• Time in Patent Office: 1,429 Days
• Field of Search: 711/141
• US Class Current: 711/141
• CPC Class Codes: G06F 12/0815 Cache consistency protocols
• CPC Class Codes: G06F 12/0817 using directory methods
• CPC Class Codes: G06F 12/0831 using a bus scheme, e.g. with bus monitoring or watching means

Abstract

A multiprocessor computer system is configured to selectively transmit address transactions through an address network using either a broadcast mode or a point-to-point mode transparent to the active devices that initiate the transactions. Depending on the mode of transmission selected, either a directory-based coherency protocol or a broadcast snooping coherency protocol is implemented to maintain coherency within the system. A computing node is formed by a group of clients which share a common address and data network. The address network is configured to determine whether a particular transaction is to be conveyed in broadcast mode or point-to-point mode. In one embodiment, the address network includes a mode table with entries which are configurable to indicate transmission modes corresponding to different regions of the address space within the node. Upon receiving a coherence request transaction, the address network may then access the table in order to determine the transmission mode, broadcast or point-to-point, which corresponds to the received transaction.

Claims

1. A multiprocessing system comprising:

a plurality of processing subsystems, each including a cache memory;

a memory subsystem including a directory;

a network interconnecting said plurality of processing subsystems and said memory subsystem;

wherein the network includes a mode unit separate from the processing subsystems and the memory subsystem, the mode unit being configured to store 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;

receive a given coherency request initiated by a requesting processing subsystem, wherein the given coherency request is not visible to other processing subsystems or the memory subsystem; and

control, in accordance with said indication, whether the given coherency request is transmitted through said network

according to a directory protocol or a broadcast protocol; and

wherein an encoding of said given coherency request excludes an indication of whether said given coherence request is to be transmitted according to said directory protocol or said broadcast protocol; and

wherein when said coherency request is transmitted through said network according to said directory protocol, said given coherency request is transmitted through said network to only said memory subsystem.

2. The multiprocessing system as recited in claim 1 wherein said directory includes a plurality of entries corresponding to different memory locations mapped to said memory subsystem, wherein each entry contains information indicative of whether a cached copy of a corresponding block has been created in one or more of said plurality of processing subsystems.

3. The multiprocessing system as recited in claim 2 wherein when said given coherency request is transmitted through said network according to said broadcast protocol, said coherency request is broadcasted to said memory subsystem and to each of said plurality of processing subsystems regardless of information contained within said directory.

4. The multiprocessing system as recited in claim 3 wherein said given coherency request is transmitted to said network through a point-to-point link.

5. The multiprocessing system as recited in claim 1 wherein when said given coherency request is transmitted through said network according to said directory protocol, said directory is accessed by said memory subsystem and responsive coherency commands are provided to one or more of said plurality of processing subsystems dependent upon information contained within said directory.

6. The multiprocessing system as recited in claim 1 wherein said mode unit includes a coherency mode storage unit configured to store an indication to control whether said given coherency request is transmitted through said network according to said directory protocol or said broadcast protocol.

7. The multiprocessing system as recited in claim 6 wherein said coherency mode storage unit is configured to store a plurality of additional indications to control whether other coherency requests are transmitted through said network according to said directory protocol or said broadcast protocol.

8. The multiprocessing system as recited in claim 7 wherein selected coherency requests are transmitted through said network according to said directory protocol while other coherency requests are transmitted through said network according to said broadcast protocol.

9. The multiprocessing system as recited in claim 8 wherein an address of each coherency request is used to dictate whether said each request is transmitted through said network according to said directory protocol or said broadcast protocol.

10. The multiprocessing system as recited in claim 1 wherein said network is implemented using a plurality of address switches.

11. 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 separate from the processing subsystems and the memory subsystem, wherein the mode unit is 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 only to said memory subsystem including 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.

12. 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 separate from the processing subsystems and the memory subsystem receiving said coherency request and indicating whether said coherency request is to be transmitted through said network according to a directory protocol or a broadcast protocol, the mode unit being configured to store an indication of whether a given block is a point-to-point mode block or a broadcast mode block, wherein the coherency request is not visible to other processing subsystems or the memory subsystem;

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, wherein when said coherency request is transmitted through said network according to said directory protocol, said given coherency request is transmitted through said network to only said memory subsystem; and

accessing a directory entry in response to said coherency request when said coherency request is transmitted through said network according to said directory protocol.

13. The method as recited in claim 12 further comprising said mode unit accessing a coherency mode storage unit that stores an indication that indicates whether said coherency request is to be transmitted through said network according to said directory protocol or said broadcast protocol.

14. A multiprocessing system comprising:

a plurality of processing subsystems;

a memory subsystem;

a network interconnecting said plurality of processing subsystems and said memory subsystem, wherein said network is configured to receive a coherency request initiated by a requesting processing subsystem, wherein the coherency request is not visible to other processing subsystems or the memory subsystem; and

a mode unit separate from the processing subsystems and the memory subsystem, the mode unit being configured to store an indication of whether a given block is a point-to-point mode block or a broadcast mode block and configured to;

control, in accordance with said indication, whether the 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; and

wherein when said coherency request is transmitted through said network according to said directory protocol, said coherency request is transmitted through said network to only said memory subsystem.

15. The multiprocessing system as recited in claim 14 wherein said mode unit includes a coherency mode storage unit configured to store an indication to control whether said coherency request is transmitted through said network according to said directory protocol or said broadcast protocol.

16. The multiprocessing system as recited in claim 15 wherein said coherency mode storage unit is configured to store a plurality of additional indications to control whether other coherency requests are transmitted through said network according to said directory protocol or said broadcast protocol.

17. The multiprocessing system as recited in claim 16 wherein selected coherency requests are transmitted through said network according to said directory protocol while other coherency requests are transmitted through said network according to said broadcast protocol.

18. The multiprocessing system as recited in claim 17 wherein an address of each coherency request is used to dictate whether said each request is transmitted through said network according to said directory protocol or said broadcast protocol.