LOAD REQUEST SCHEDULING IN A CACHE HIERARCHY

• US 20100268882A1
• Filed: 04/15/2009
• Published: 10/21/2010
• Est. Priority Date: 04/15/2009
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Powell, Stephen James, Stuecheli, Jeffrey A., Starke, William John, Guthrie, Guy Lynn, Cargnoni, Robert Alan
• Granted Patent: US 8,521,982 B2
• Time in Patent Office: Days
• US Class Current: 711/122
• CPC Class Codes: G06F 12/084 with a shared cache
• CPC Class Codes: G06F 12/0897 with two or more cache hierarchy levels with multilevel cache hierarchies G06F12/0811
• CPC Class Codes: G06F 12/123 with age lists, e.g. queue, most recently used [MRU] list or least recently used [LRU] list
• CPC Class Codes: G06F 2212/1024 Latency reduction

Abstract

A system and method for tracking core load requests and providing arbitration and ordering of requests. When a core interface unit (CIU) receives a load operation from the processor core, a new entry in allocated in a queue of the CIU. In response to allocating the new entry in the queue, the CIU detects contention between the load request and another memory access request. In response to detecting contention, the load request may be suspended until the contention is resolved. Received load requests may be stored in the queue and tracked using a least recently used (LRU) mechanism. The load request may then be processed when the load request resides in a least recently used entry in the load request queue. CIU may also suspend issuing an instruction unless a read claim (RC) machine is available. In another embodiment, CIU may issue stored load requests in a specific priority order.

Claims

1. A method of data processing in a processing unit, including a processor core, an upper level cache memory, and a lower level cache memory, the method comprising:

in response to receiving a load-type request issued of the processor core at the lower level cache memory, allocating an entry among a plurality of entries in a request queue of the lower level cache memory to the load-type request;

detecting contention for one or more resources between the load-type request and another memory access request in the processing unit;

in response to detecting contention for at least one of the one or more resources, suspending issuance of the load-type request from the entry of the request queue until the contention is resolved; and

in response to removal of the contention, issuing the load-type request from the request queue for processing by the lower level cache memory.

2. The method of claim 1, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention.

3. The method of claim 1, wherein the load-type request is a store request, further comprising:

dynamically tracking processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminating tracking of the load-type request.

4. The method of claim 1, further comprising:

tracking a plurality of received load-type requests in the plurality of entries in the queue with a least recently used (LRU) mechanism; and

issuing the load request in the entry of the queue only if the load request resides in a least recently used non-suspended entry among the plurality of entries in the queue.

5. A method of data processing in a processing unit, including a processor core, an upper level cache memory, and a lower level cache memory, the method comprising:

in response to receiving a load request issued of the processor core at the lower level cache memory, allocating an entry among a plurality of entries in a request queue of the lower level cache memory to the load request;

tracking a plurality of received load requests in the plurality of entries of the queue with a least recently used (LRU) mechanism; and

issuing the load request from the entry of the queue for processing in the lower level cache memory when the load request resides in a least recently used entry among the plurality of entries in the queue.

6. The method of claim 5, further comprising:

detecting contention for one or more resources between the load request and another memory access request in the processing unit;

in response to detecting contention for at least one of the one or more resources, suspending processing of the load request in the entry of the queue until the contention is resolved; and

updating a tracking information of the load request in the queue, wherein the tracking information may include read claim (RC) number.

7. The method of claim 6, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention.

8. The method of claim 5, wherein the load-type request is a store request, further comprising:

dynamically tracking processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminating tracking of the load-type request.

9. A data processing system, comprising:

a local processor core;

a cache memory coupled to the local processor core; and

processing logic executing on the processor core for enabling the data processing system to perform the steps of;

in response to receiving a load-type request issued of the processor core at the lower level cache memory, allocating an entry among a plurality of entries in a request queue of the lower level cache memory to the load-type request;

detecting contention for one or more resources between the load-type request and another memory access request in the processing unit;

in response to detecting contention for at least one of the one or more resources, suspending issuance of the load-type request from the entry of the request queue until the contention is resolved; and

in response to removal of the contention, issuing the load-type request from the request queue for processing by the lower level cache memory.

10. The data processing system of claim 9, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention.

11. The data processing system of claim 9, wherein the load-type request is a store request, further comprising:

dynamically tracking processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminating tracking of the load-type request.

12. The data processing system of claim 9, further comprising:

tracking a plurality of received load-type requests in the plurality of entries in the queue with a least recently used (LRU) mechanism; and

issuing the load request in the entry of the queue only if the load request resides in a least recently used non-suspended entry among the plurality of entries in the queue.

13. A data processing system, comprising:

a local processor core;

a cache memory coupled to the local processor core; and

processing logic executing on the processor core for enabling the data processing system to perform the steps of;

in response to receiving a load request issued of the processor core at the lower level cache memory, allocating an entry among a plurality of entries in a request queue of the lower level cache memory to the load request;

tracking a plurality of received load requests in the plurality of entries of the queue with a least recently used (LRU) mechanism; and

issuing the load request from the entry of the queue for processing in the lower level cache memory when the load request resides in a least recently used entry among the plurality of entries in the queue.

14. The data processing system of claim 13, further comprising:

detecting contention for one or more resources between the load request and another memory access request in the processing unit;

in response to detecting contention for at least one of the one or more resources, suspending processing of the load request in the entry of the queue until the contention is resolved; and

updating a tracking information of the load request in the queue, wherein the tracking information may include read claim (RC) number.

15. The data processing system of claim 14, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention.

16. The data processing system of claim 13, wherein the load-type request is a store request, further comprising:

dynamically tracking processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminating tracking of the load-type request.

17. A computer-readable storage medium having a plurality of instructions embodied therein, wherein the plurality of instructions, when executed by a processing device, allows a machine to:

in response to receiving a load-type request issued of the processor core at the lower level cache memory, allocate an entry among a plurality of entries in a request queue of the lower level cache memory to the load-type request;

detecting contention for one or more resources between the load-type request and another memory access request in the processing unit;

in response to detect contention for at least one of the one or more resources, suspending issuance of the load-type request from the entry of the request queue until the contention is resolved, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention; and

in response to removal of the contention, issue the load-type request from the request queue for processing by the lower level cache memory.

18. The computer-readable storage medium of claim 17, wherein the load-type request is a store request, the plurality of instructions further comprising:

dynamically track processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminate tracking of the load-type request.

19. A computer-readable storage medium having a plurality of instructions embodied therein, wherein the plurality of instructions, when executed by a processing device, allows a machine to:

in response to receiving a load request issued of the processor core at the lower level cache memory, allocating an entry among a plurality of entries in a request queue of the lower level cache memory to the load request;

tracking a plurality of received load requests in the plurality of entries of the queue with a least recently used (LRU) mechanism;

issuing the load request from the entry of the queue for processing in the lower level cache memory when the load request resides in a least recently used entry among the plurality of entries in the queue;

detect contention for one or more resources between the load request and another memory access request in the processing unit;

in response to detecting contention for at least one of the one or more resources, suspend processing of the load request in the entry of the queue until the contention is resolved, wherein the suspending further comprises, setting a suspend bit of the entry for the duration of the contention; and

update a tracking information of the load request in the queue, wherein the tracking information may include read claim (RC) number.

20. The computer-readable storage medium of claim 19, wherein the load-type request is a store request, the plurality of instructions further comprising:

dynamically track processing of the load-type request to a RC machine; and

in response to detecting the completion of migration of the load-type request to the specific RC machine, terminate tracking of the load-type request.