Multi-node data processing system and method of queue management in which a queued operation is speculatively cancelled in response to a partial combined response

• US 6,591,307 B1
• Filed: 11/09/1999
• Issued: 07/08/2003
• Est. Priority Date: 11/09/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Fields, James Stephen Jr., Arimilli, Ravi Kumar, Guthrie, Guy Lynn, Joyner, Jody Bern, Lewis, Jerry Don
• Primary Examiner(s): Sheikh, Ayaz
• Assistant Examiner(s): WON, MICHAEL YOUNG
• Application Number:
  US09/436,897
• Time in Patent Office: 1,337 Days
• Field of Search: 709/201, 709/202, 709/220, 709/400, 709/232, 711/146, 711/118, 711/141, 712/28
• US Class Current: 713/375
• CPC Class Codes: G06F 12/0813 with a network or matrix configuration
• CPC Class Codes: G06F 12/0815 Cache consistency protocols
• CPC Class Codes: G06F 12/0831 using a bus scheme, e.g. with bus monitoring or watching means

Abstract

A data processing system includes an interconnect, a plurality of nodes coupled to the interconnect that each include at least one agent, response logic within each node, and a queue. In response to snooping a transaction on the interconnect, each agent outputs a snoop response. In addition, the queue, which has an associated agent, allocates an entry to service the transaction. The response logic within each node accumulates a partial combined response of its node and any preceding node until a complete combined response for all of the plurality of nodes is obtained. However, prior to the associated agent receiving the complete combined response, the queue speculatively deallocates the entry if the partial combined response indicates that an agent other than the associated agent will service the transaction.

Claims

1. A data processing system, comprising:

an interconnect;

a plurality of nodes coupled to said interconnect, wherein each of said plurality of nodes includes at least one agent and at least one of said plurality of nodes includes multiple agents, wherein each agent in all of said plurality of nodes snoops a transaction transmitted on said interconnect and outputs a snoop response in response to snooping the transaction;

response logic within each node that accumulates a partial combined response to said transaction, said partial combined response representing a combination of the snoop response of each agent within its node and a partial combined response of any preceding node, wherein the response logic within anode among said plurality of nodes accumulates a partial combined response of one or more preceding nodes with the snoop response of each of one or more agents within its node to obtain a complete combined response to the transaction of all agents within all of said plurality of nodes, and wherein said response logic of the node provides said complete combined response to all of said plurality of nodes; and

a queue that, responsive to an associated agent snooping the transaction, allocates an entry to service said transaction, wherein said queue speculatively deallocates said entry prior to receipt of said complete combined response by said associated agent in response to a partial combined response indicating that an agent other said associated agent will service said transaction.

2. The data processing system of claim 1, and further comprising a memory controller coupled to said associated agent, said memory controller containing said queue.

3. The data processing system of claim 2, wherein said transaction is a read request and said partial combined response indicates that a preceding node contains an agent having a higher sourcing priority.

4. The data processing system of claim 1, said plurality of nodes including a mastering node containing a mastering agent that issued said transaction, wherein response logic within said mastering node provides said complete combined response to all of said plurality of nodes.

5. The data processing system of claim 1, wherein said interconnect comprises:

a plurality of address channels, wherein each agent in all of said plurality of nodes is coupled to all of said plurality of address channels, and wherein each agent can only master transactions on an address channel associated with its node and snoops transactions on all of said plurality of address channels; and

at least one data channel.

6. The data processing system of claim 1, wherein said plurality of nodes includes at least three nodes, and wherein said interconnect includes an address portion that couples said plurality of nodes in a ring topology.

7. The data processing system of claim 6, wherein:

said plurality of nodes sequentially receive said transaction from said interconnect; and

said response logic produces said partial combined response to said transaction for its node based upon snoop responses of agents in its node and any node previously receiving the transaction on said interconnect.

8. A method of communication in a data processing system including an interconnect coupling a plurality of nodes that each include at least one agent and response logic, wherein at least one of said plurality of nodes includes a plurality of agents, said method comprising:

in response to snooping a transaction transmitted on said interconnect, outputting, from each agent, a snoop response and, at a queue having an associated agent, allocating an entry to service said transaction;

utilizing the response logic of each node, accumulating a partial combined response of the node and any preceding node until a complete combined response to said transaction for all of agents in all of said plurality of nodes is obtained, said partial combined response of each node representing a combination of the snoop response of each agent within that node and a partial combined response of any preceding node;

providing said complete combined response to all of said plurality of nodes; and

prior to receipt of said complete combined response by said associated agent, speculatively deallocating said entry in response to a partial combined response indicating that an agent other said associated agent will service said transaction.

9. The method of claim 8, said data processing system further comprising a memory controller coupled to said associated agent, said memory controller containing said queue, wherein said step of allocating an entry to service said transaction comprises allocating an entry within said queue contained in said memory controller.

10. The method of claim 9, wherein said transaction is a read request, and wherein speculatively deallocating said entry comprises:

speculative deallocating said entry in response to said partial combined response indicating that a preceding node contains an agent having a higher sourcing priority.

11. The method of claim 8, said plurality of nodes including a mastering node containing a mastering agent that issued said transaction, wherein providing said complete combined response comprises providing said complete combined response to all of said plurality of nodes from response logic within said mastering node.

12. The method of claim 8, wherein said interconnect comprises a plurality of address channels and at least one data channel, said method further comprising:

coupling each agent in all of said plurality of nodes to all of said plurality of address channels and to said at least one data channel, such that each agent can only master transactions on an address channel associated with its node and snoops transactions on all of said plurality of address channels.

13. The method of claim 8, wherein said plurality of nodes includes at least three nodes, and wherein said interconnect includes an address portion, said method further comprising coupling said plurality of nodes in a ring topology with said address portion of said interconnect.

14. The method of claim 13, wherein:

said method further comprises said plurality of nodes sequentially receiving said transaction from said interconnect; and

said accumulating step comprises response logic within each node producing a partial combined response to said transaction for its node based upon snoop responses of agents in its node and any node previously receiving the transaction on said interconnect.