Distributed caching mechanism for pending memory operations within a memory controller

• US 20030204684A1
• Filed: 04/25/2002
• Published: 10/30/2003
• Est. Priority Date: 04/25/2002
• Status: Active Grant

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Schulz, Jurgen M., Stratman, David C.
• Granted Patent: US 6,959,361 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• CPC Class Codes: G06F 12/084 with a shared cache

Abstract

One embodiment of the present invention provides a memory controller that contains a distributed cache that stores cache lines for pending memory operations. This memory controller includes an input that receives memory operations that are directed to an address in memory. It also includes a central scheduling unit and multiple agents that operate under control of the central scheduling unit. Upon receiving a current address, a given agent compares the current address with a cache line stored within the given agent. All of the agents compare the current address with their respective cache line in parallel. If the addresses match, the agent reports the result to the rest of the agents in the memory controller, and accesses data within the matching cache line stored within the agent to accomplish the memory operation.

Claims

1. A memory controller containing a distributed cache that stores cache lines for pending memory operations, comprising:

an input mechanism that is configured to receive a memory operation that is directed to a current address in memory;

a central scheduling unit;

a plurality of agents under control of the central scheduling unit, wherein a given agent in the plurality of agents is configured to receive the current address;

a comparison mechanism within the given agent that is configured to compare the current address with an address of a cache line stored within the given agent;

a reporting mechanism within the given agent that is configured to report to the plurality of agents a result provided by the comparison mechanism; and

an access mechanism that is configured to access data within the cache line stored within the given agent in order to accomplish the memory operation when the comparison mechanism indicates a match;

wherein the plurality of agents compare the current address with their respective cache line addresses in parallel; and

wherein the given agent holds the cache line while memory operations are pending for the cache line.

2. The memory controller of claim 1, further comprising a queue within the given agent that provides storage for pending memory operations that are waiting for memory operations directed to the cache line stored within the given agent to complete.

3. The memory controller of claim 2, further comprising a memory write mechanism that is configured to write the cache line stored within the given agent to memory after a last entry in the queue has been processed, wherein the given agent is free to be associated with a new cache line when writing is complete.

4. The memory controller of claim 3, further comprising a status mechanism within the given agent to provide status information to the central scheduling unit indicating whether the given agent is currently associated with the cache line or is free to be associated with the new cache line.

5. The memory controller of claim 4, wherein the given agent can respond to the address matching the cache line when the given agent is free to be associated with the new cache line.

6. The memory controller of claim 1, wherein the comparison mechanism is further configured to abort comparing the address with the cache line if another agent reports a match.

7. The memory controller of claim 1, further comprising an allocating unit within the given agent that is configured to allocate the given agent to the address when the central scheduling unit signals that the given agent is next to be allocated.

8. A method that facilitates distributed caching within a memory controller, the method comprising:

receiving at a given agent in a plurality of agents a memory operation that is directed to a current address in memory;

comparing the current address with an address of a cache line stored within the given agent;

reporting to the plurality of agents a result of comparing the address; and

if the comparison indicates a match, accessing data within the cache line stored within the given agent in order to accomplish the memory operation;

wherein the plurality of agents compare the current address with the address of their respective cache lines in parallel; and

wherein the given agent holds the cache line while memory operations are pending for the cache line.

9. The method of claim 8, further comprising queuing within the given agent a plurality of pending memory operations that are waiting for a memory operation involving the cache line to complete.

10. The method of claim 9, further comprising writing data stored within the given agent to memory after a last entry in a queue within the given agent has been processed, wherein the given agent is free to be associated with a new cache line when writing is complete.

11. The method of claim 10, further comprising providing status information to a central scheduling unit indicating whether the given agent is currently associated with the cache line or is free to be associated with the new cache line.

12. The method of claim 11, wherein the given agent can respond to the address matching the cache line when the given agent is free to be associated with the new cache line.

13. The method of claim 8, further comprising aborting comparing the address with the cache line if another agent reports a match.

14. The method of claim 8, further comprising allocating the given agent to the address when a central scheduling unit signals that the given agent is next to be allocated.

15. An integrated circuit that includes a distributed cache, comprising:

an input mechanism that is configured to receive a memory operation that is directed to a current address in memory;

a central scheduling unit;

a plurality of agents under control of the central scheduling unit, wherein a given agent in the plurality of agents is configured to receive the current address;

a comparison mechanism within the given agent that is configured to compare the current address with an address to a cache line stored within the given agent;

a reporting mechanism within the given agent that is configured to report to the plurality of agents a result provided by the comparison mechanism; and

an access mechanism that is configured to access the cache line stored within the given agent in order to accomplish the memory operation when the comparison mechanism indicates a match;

wherein the plurality of agents compare the current address with addresses of their respective cache lines in parallel; and

wherein the given agent holds data within the cache line while memory operations are pending for the cache line.

16. The integrated circuit of claim 15, further comprising a queue within the given agent that provides storage for pending memory operations that are waiting for a memory operation involving the cache line to complete.

17. The integrated circuit of claim 16, further comprising a memory write mechanism that is configured to write data stored within the given agent to memory after a last entry in the queue has been processed, wherein the given agent is free to be associated with a new cache line when writing is complete.

18. The integrated circuit of claim 17, further comprising a status mechanism within the given agent to provide status information to the central scheduling unit indicating whether the given agent is currently associated with the cache line or is free to be associated with the new cache line.

19. The integrated circuit of claim 18, wherein the given agent can respond to the address matching the cache line when the given agent is free to be associated with the new cache line.

20. The integrated circuit of claim 15, wherein the comparison mechanism is further configured to abort comparing the address with the cache line if another agent reports a match.

21. The integrated circuit of claim 15, further comprising an allocating unit within the given agent that is configured to allocate the given agent to the address when the central scheduling unit signals that the given agent is next to be allocated.