System and method for snooping cache information using a directory crossbar

• US 20060174069A1
• Filed: 01/31/2005
• Published: 08/03/2006
• Est. Priority Date: 01/31/2005
• Status: Active Grant

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Shaw, Mark, Berke, Stuart Allen
• Granted Patent: US 8,205,046 B2
• Time in Patent Office: Days
• US Class Current: 711/146
• CPC Class Codes: G06F 12/0817 using directory methods

Abstract

A system and method for maintaining coherency in a symmetric multiprocessing (SMP) system are disclosed. Briefly described, in architecture, one exemplary embodiment comprises a first crossbar coupled to a plurality of local processors; a second crossbar coupled to at least one remote processor; and at least one crossbar directory that tracks access of information by a remote processor in a symmetric multiprocessing (SMP) system, the remote processor in communication with at least one of the local processors via the crossbars, such that a most current location of the information can be determined by the crossbar directory.

Claims

1. A directory crossbar system, comprising:

a first crossbar coupled to a plurality of local processors;

a second crossbar coupled to at least one remote processor; and

at least one crossbar directory that tracks access of information by a remote processor in a symmetric multiprocessing (SMP) system, the remote processor in communication with at least one of the local processors via the crossbars, such that a most current location of the information can be determined by the crossbar directory.

2. The directory crossbar system of claim 1, wherein the crossbar directory determines that the remote processor has ownership of the information.

3. The directory crossbar system of claim 1, wherein the crossbar directory resides in the second crossbar coupled to the remote processor such that in response to a subsequent snoop, the crossbar directory indicates that the remote processor currently owns the information.

4. The directory crossbar system of claim 1, wherein the crossbar directory resides in the first crossbar coupled to the plurality of local processors such that in response to a subsequent snoop, the crossbar directory indicates that the remote processor currently owns the information.

5. The directory crossbar system of claim 1, wherein the crossbar directory further comprises:

a processing unit;

a cache residing in the processing unit; and

a database residing on the cache wherein data corresponding to the most current location of the information resides.

6. The directory crossbar system of claim 1, wherein the crossbar directory further comprises:

a processing unit;

a memory coupled to the processing unit; and

a database residing on the memory wherein data corresponding to the most current location of the information resides.

7. The directory crossbar system of claim 6, wherein the memory further comprises at least one dual in-line memory module (DIMM).

8. The directory crossbar system of claim 1, wherein the crossbar directory further comprises:

a directory controller;

a directory memory coupled to the directory controller; and

a database residing on the directory memory wherein data corresponding to the most current location of the information resides.

9. The directory crossbar system of claim 8, wherein the directory memory further comprises at least one dual in-line memory module (DIMM).

10. The directory crossbar system of claim 1, further comprising:

a plurality of crossbars; and

a global crossbar directory integrated with each one of the crossbars, such that receipt of the information by the remote processor is indicated in a database of the global crossbar directory, and wherein in response to a subsequent snoop, the global crossbar directory indicates the most current location of the information.

11. The directory crossbar system of claim 1, further comprising:

a plurality of crossbars; and

a plurality of crossbar directories, one of the crossbar directories residing in one of the crossbars, such that receipt of the information by the remote processor is indicated in a database of the crossbar directory, and wherein in response to a subsequent snoop, the crossbar directory indicates to at least one other crossbar directory that the remote processor has current ownership of the information.

12. The directory crossbar system of claim 11, wherein the subsequent snoop originates from a requesting CPU.

13. The directory crossbar system of claim 1, further comprising the symmetric multiprocessing (SMP) system wherein the directory crossbar system resides.

14. A directory crossbar system, comprising:

a plurality of crossbars; and

a global crossbar directory integrated with each one of the crossbars, and coupled to a plurality of processors such that ownership of information by a destination processor coupled to the crossbar directory is indicated in a database of the global crossbar directory, and wherein in response to a subsequent snoop from a requesting processor, the global crossbar directory indicates that the destination processor has current ownership of the information.

15. The directory crossbar system of claim 14, wherein the global crossbar directory further comprises:

a processing unit;

a cache residing in the processing unit; and

the database residing on the cache such that ownership of the information by the destination processor coupled to the global crossbar directory is indicated in the database.

16. The directory crossbar system of claim 14, wherein the global crossbar directory further comprises:

a processing unit;

a memory coupled to the processing unit; and

the database residing on the memory such that ownership of the information by the destination processor coupled to the global crossbar directory is indicated in the database.

17. The directory crossbar system of claim 14, wherein the global crossbar directory further comprises:

a directory controller;

a directory memory coupled to the directory controller; and

the database residing on the directory memory such that ownership of the information by the destination processor coupled to the global crossbar directory is indicated in the database.

18. The directory crossbar system of claim 14, wherein the global crossbar directory communicates the subsequent snoop to other processors residing in a processor cluster with the requesting processor, wherein the global crossbar directory then receives status information from the other processors corresponding to previous ownership of the information of interest by the other processors, and wherein the global crossbar directory then determines the most currently available information of interest by comparing the status information from the other processors and the ownership information indicated in the database.

19. The directory crossbar system of claim 14, further comprising a symmetric multiprocessing (SMP) system wherein the directory crossbar system resides.

20. A method for maintaining coherency in a symmetric multiprocessing (SMP) system, comprising:

receiving from a requesting processor a snoop to determine location of a most current information of interest, the snoop received by a crossbar directory integrated with a crossbar;

communicating a subsequent snoop to at least one other crossbar directory integrated with another crossbar; and

receiving a response from the other crossbar directory to the subsequent snoop, the response indicating that a remote processor coupled to the other crossbar directory has current ownership of the information of interest.

21. The method of claim 20, further comprising communicating the information of interest from the remote processor to the requesting processor.

22. The method of claim 20, wherein communicating the subsequent snoop further comprises:

communicating the subsequent snoop to other processors residing in a processor cluster with the requesting processor;

receiving status information from the other processors corresponding to previous ownership of the information of interest by the other processors;

determining the most currently available information of interest by comparing the status information from the other processors and the response received from the responding crossbar directory.

23. The method of claim 22, wherein receiving the status information from the other processors further comprises receiving the information of interest.

24. The method of claim 20, wherein the remote processor resides in an input/output (I/O) device.

25. A method for maintaining coherency in a symmetric multiprocessing (SMP) system with a global crossbar directory integrated with a plurality of crossbars, comprising:

tracking ownership of information of interest accessed by a remote processor, the information of interest provided by a first processor;

receiving from a requesting processor a snoop to determine location of a most current version of the information of interest, the snoop received by the global crossbar directory;

communicating a subsequent snoop from the global crossbar directory to other processors residing in a processor cluster commonly with the requesting processor;

receiving status information from the other processors corresponding to previous access of the information of interest by the other processors; and

determining the most currently available information of interest by comparing the status information from the other processors and the access information.

26. The method of claim 25, wherein receiving the status information from the other processors further comprises receiving the information of interest.

27. The method of claim 25, wherein tracking access of information further comprises storing the ownership information in a processor cache.

28. The method of claim 25, wherein tracking the access of information further comprises storing the access information in a memory coupled to a processor that performs the tracking, receiving, communicating and determining.

29. A system for maintaining coherency in a symmetric multiprocessing (SMP) system with a global crossbar directory integrated with a plurality of crossbars, comprising:

means for tracking ownership of information of interest owned by a remote central processing unit (CPU), the information of interest provided by a first CPU;

means for receiving from a requesting CPU a snoop to determine location of a most current version of the information of interest;

means for communicating a subsequent snoop to other CPUs residing in a CPU cluster commonly with the requesting CPU;

means for receiving status information from the other CPUs corresponding to previous ownership of the information of interest by the other CPUs; and

means for determining the most currently available information of interest by comparing the status information from the other CPUs and the access information.