Cache coherency arrangement to enhance inbound bandwidth

• US 6,842,827 B2
• Filed: 01/02/2002
• Issued: 01/11/2005
• Est. Priority Date: 01/02/2002
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Lambert, Matthew A., Blankenship, Robert G., Rand, Tony S.
• Primary Examiner(s): LANE, JOHN A
• Application Number:
  US10/038,996
• Publication Number:
  US 20030126376A1
• Time in Patent Office: 1,105 Days
• Field of Search: 711/141, 711/146, 711/137, 710/39, 710/40
• US Class Current: 711/141
• CPC Class Codes: G06F 12/0835 for main memory peripheral accesses (e.g. I/O or DMA)

Abstract

A cache coherency arrangement with support for pre-fetch ownership, to enhance inbound bandwidth for single leaf and multiple leaf, input-output interfaces, with shared memory space is disclosed. Embodiments comprise ownership stealing to enhance inbound bandwidth and to prevent or attenuate starvation of transactions or of an input-output interface for transactions.

Claims

1. An apparatus, comprising:

a snoop filter to determine a conflict associated with an ownership of a memory line;

a hub interface coupled with said snoop filter to maintain a transaction order for an upbound transaction associated with the ownership, from an input-output interface, and to determine a coherency state for the upbound transaction based upon the conflict and the transaction order, to take the ownership from the upbound transaction; and

an upbound path coupled with said hub interface to transmit the upbound transaction to an unordered interface.

2. The apparatus of claim 1, further comprising a coherency interface coupled with said snoop filter to transmit a coherency request to said hub interface.

3. The apparatus of claim 1, wherein said snoop filter comprises conflict circuitry coupled with said upbound path to determine the conflict between the ownership by the upbound transaction and a downbound snoop request.

4. The apparatus of claim 1, wherein said snoop filter comprises conflict circuitry coupled with said hub interface to determine the conflict between the ownership by the upbound transaction and a request associated with an inbound transaction.

5. The apparatus of claim 1, wherein said snoop filter comprises conflict circuitry coupled with said upbound path to determine the conflict between a request for the ownership by the upbound transaction and the ownership by a pending upbound transaction on the unordered interface.

6. The apparatus of claim 1, wherein said hub interface comprises an upbound ordering queue to store a transaction header of the upbound transaction and to maintain the transaction order.

7. The apparatus of claim 1, wherein said hub interface comprises a coherency circuit coupled with said snoop filter to determine a coherency state for the upbound transaction.

8. The apparatus of claim 7, wherein the coherency circuit comprises circuitry coupled with said snoop filter to invalidate the coherency state of exclusive ownership of a memory line by the upbound transaction.

9. The apparatus of claim 1, wherein said hub interface comprises a starvation prevention circuit to limit a number of invalidations to send to the upbound transaction.

10. The apparatus of claim 1, wherein said upbound path comprises a pending transaction buffer to store a pending, upbound transaction on the unordered interface.

11. A method, comprising:

maintaining a transaction order for an upbound transaction based upon an ordering of an input-output interface to transmit the upbound transaction to an unordered interface;

determining a conflict associated with an ownership of a memory line by the upbound transaction; and

determining a coherency state for the upbound transaction based upon the conflict and the transaction order, to take the ownership from the upbound transaction.

12. The method of claim 11, further comprising limiting a number of invalidations to send to the upbound transaction to prevent starvation.

13. The method of claim 12, wherein limiting comprises stalling the input-output interface to transmit the upbound transaction to the unordered interface.

14. The method of claim 11, wherein said maintaining comprises placing the upbound transaction in a queue.

15. The method of claim 11, wherein said determining a conflict comprises determining the conflict between the ownership by the upbound transaction and a request by an inbound read transaction.

16. The method of claim 11, wherein said determining a conflict comprises determining the conflict between the ownership by the upbound transaction and an inbound ownership request from a second input-output interface.

17. The method of claim 11, wherein said determining a conflict comprises determining the conflict between the ownership by the upbound transaction and a downbound snoop request.

18. The method of claim 11, wherein said determining a conflict comprises determining the conflict between a request for the ownership by the upbound transaction and the ownership by a pending inbound transaction on the unordered interface.

19. The method of claim 11, wherein said determining a coherency state comprises applying back-pressure to subsequent read transactions from input-output devices until the conflict is cleared.

20. The method of claim 11, wherein said determining a coherency state comprises issuing an invalidation request for the upbound transaction.

21. The method of claim 20, wherein said determining a coherency state further comprises rejecting an invalidation request for the upbound transaction, wherein the upbound transaction is near the top of a queue.

22. The method of claim 11, wherein said determining a coherency state comprises:

changing the coherency state of the upbound transaction from exclusive to steal the ownership from the upbound transaction; and

reissuing a request for the ownership by the upbound transaction.

23. The method of claim 22, wherein said determining a coherency state further comprises sending an inbound read transaction upbound.

24. The method of claim 22, wherein said determining a coherency state further comprises issuing an invalid response to a downbound snoop request.

25. A system, comprising:

a snoop filter to determine a conflict associated with an ownership of a memory line;

a hub interface coupled with said snoop filter to maintain a transaction order for an upbound transaction associated with the ownership, from an input-output interface, and to determine a coherency state for the upbound transaction based upon the conflict and the transaction order, to take the ownership from the upbound transaction;

an upbound path coupled with said hub interface to transmit the upbound transaction to an unordered interface;

a memory circuit coupled with said upbound path to store data on a memory line associated with the upbound transaction; and

a input-output device coupled with said hub interface to transmit the upbound transaction to access said memory circuit.

26. The system of claim 25, further comprising a scalability port switch coupled with the unordered interface to direct a transaction from a second input-output hub.

27. The system of claim 25, wherein said input-output device comprises a bridge coupled with said hub interface to couple more than one input-output device with said hub interface.

28. A machine-readable medium containing instructions, which when executed by a machine, cause said machine to perform operations, comprising:

maintaining a transaction order for an upbound transaction based upon an ordering of an input-output interface to transmit the upbound transaction to an unordered interface;

determining a conflict associated with an ownership of a memory line by the upbound transaction; and

determining a coherency state for the upbound transaction based upon the conflict and the transaction order, to take the ownership from the upbound transaction.

29. The machine-readable medium of claim 28, further comprising pre-fetching the ownership for the upbound transaction.

30. The machine-readable medium of claim 28, wherein said determining a coherency state comprises:

changing the coherency state of the upbound transaction from exclusive to steal the ownership from the upbound transaction; and

reissuing a request for the ownership by the upbound transaction.