Cache snooping mode extending coherence protection for certain requests

Patent metadata

Field	Value
Publication number	US-11157408-B2
Application number	US-201916717835-A
Country	US
Kind code	B2
Filing date	Dec 17, 2019
Priority date	Dec 17, 2019
Publication date	Oct 26, 2021
Grant date	Oct 26, 2021

Abstract

A cache memory includes a data array, a directory of contents of the data array that specifies coherence state information, and snoop logic that processes operations snooped from a system fabric by reference to the data array and the directory. The snoop logic, responsive to snooping on the system fabric a request of a flush or clean memory access operation of an initiating coherence participant, determines whether the directory indicates the cache memory has coherence ownership of a target address of the request. Based on determining the directory indicates the cache memory has coherence ownership of the target address, the snoop logic provides a coherence response to the request that causes coherence ownership of the target address to be transferred to the initiating coherence participant, such that the initiating coherence participant can protect the target address against conflicting requests.

First claim

What is claimed is:

1. A cache memory of an associated processor core among a plurality of processor cores in a multiprocessor data processing system, said multiprocessor data processing system including a system fabric communicatively coupling the cache memory and a memory controller of a system memory to receive operations on the system fabric, the cache memory comprising:
a data array;
a directory of contents of the data array, wherein the directory includes coherence state information; and
snoop logic that processes operations snooped from the system fabric by reference to the data array and the directory, wherein the snoop logic, responsive to snooping on the system fabric a request of a flush or clean memory access operation of an initiating coherence participant, the request specifying a target address:
determines whether the directory indicates the cache memory has coherence ownership of the target address;
based on determining the directory indicates the cache memory has coherence ownership of the target address, provides a coherence response to the request that causes coherence ownership of the target address to be transferred to the initiating coherence participant, such that the initiating coherence participant can protect the target address against conflicting requests.

2. The cache memory of claim 1 , wherein the snoop logic is configured to protect the target address against conflicting memory access requests by issuing Retry coherence responses to the conflicting memory access requests.

3. The cache memory of claim 2 , wherein the snoop logic, responsive to completing processing of the request, ends its protection of the target address.

4. The cache memory of claim 1 , wherein the cache memory provides the coherence response based on the directory indicating a copy of a memory block associated with the target address that is held in the data array is modified with respect to the system memory.

5. The cache memory of claim 1 , wherein the memory access operation is a flush operation that causes any modified data associated with the target address to written to the system memory and any cached copies of a memory block associated with the target address to be invalidated.

6. A processing unit, comprising:
a cache memory according to claim 1 ; and
at least one affiliated processor core coupled to the cache memory.

7. A data processing system, comprising:
a system fabric; and
a plurality of processing units according to claim 5 all coupled to the system fabric.

8. A design structure tangibly embodied in a machine-readable storage device for designing, manufacturing, or testing an integrated circuit, the design structure comprising:
a processing unit, including:
a processor core;
a cache memory including:
a data array;
a directory of contents of the data array, wherein the directory includes coherence state information; and
snoop logic that processes operations snooped from the system fabric by reference to the data array and the directory, wherein the snoop logic, responsive to snooping on the system fabric a request of a flush or clean memory access operation of an initiating coherence participant, the request specifying a target address:
determines whether the directory indicates the cache memory has coherence ownership of the target address;
based on determining the directory indicates the cache memory has coherence ownership of the target address, provides a coherence response to the request that causes coherence ownership of the target address to be transferred to the initiating coherence participant, such that the initiating coherence participant can protect the target address against conflicting requests.

9. The design structure of claim 8 , wherein the snoop logic is configured to protect the target address against conflicting memory access requests by issuing Retry coherence responses to the conflicting memory access requests.

10. The design structure of claim 9 , wherein the snoop logic, responsive to completing processing of the request, ends its protection of the target address.

11. The design structure of claim 8 , wherein the cache memory provides the coherence response based on the directory indicating a copy of a memory block associated with the target address that is held in the data array is modified with respect to the system memory.

12. The design structure of claim 8 , wherein the memory access operation is a flush operation that causes any modified data associated with the target address to written to the system memory and any cached copies of a memory block associated with the target address to be invalidated.

13. A method of data processing in a multiprocessor data processing system including a cache memory of an associated processor core among a plurality of processor cores in the multiprocessor data processing system, said multiprocessor data processing system including a system fabric communicatively coupling the cache memory and a memory controller of a system memory to receive operations on the system fabric, the method comprising:
the cache memory snooping, on the system fabric, a request of a flush or clean memory access operation of an initiating coherence participant, the request specifying a target address;
responsive to snooping the request, the cache memory determining whether a directory of the cache memory indicates the cache memory has coherence ownership of the target address; and
based on determining the directory indicates the cache memory has coherence ownership of the target address, the cache memory providing a coherence response to the request that causes coherence ownership of the target address to be transferred to the initiating coherence participant, such that the initiating coherence participant can protect the target address against conflicting requests.

14. The method of claim 13 , and further comprising:
the cache memory protecting the target address against conflicting memory access requests by issuing Retry coherence responses to the conflicting memory access requests.

15. The method of claim 14 , and further comprising:
the cache memory, responsive to completing processing of the request, ending its protection of the target address.

16. The method of claim 13 , wherein the cache memory provides the coherence response based on the directory indicating a copy of a memory block associated with the target address that is held in the data array is modified with respect to the system memory.

17. The method of claim 13 , wherein:
the initiating coherence participant, responsive to receipt of coherence ownership of the target address, issuing at least one cleanup command on the system fabric to cause update of system memory with modified data associated with the target address.

18. The method of claim 17 , wherein:
the request is a request of a flush memory access operation that requests that any modified data associated with the target address to written to the system memory and any cached copies of a memory block associated with the target address to be invalidated; and
the at least one cleanup command further causes invalidation of at least one cached copy of a memory block associated with the target address.

Assignees

• IBM

Inventors

• Williams Derek E
• Guthrie Guy L
• Shen Hugh
• Murray Luke

Classifications

• G06F12/0828 Primary

  with concurrent directory accessing, i.e. handling multiple concurrent coherency transactions · CPC title

• G06F12/0831 Primary

  using a bus scheme, e.g. with bus monitoring or watching means · CPC title

• G06F12/0824

  Distributed directories, e.g. linked lists of caches · CPC title

• G06F12/0842

  for multiprocessing or multitasking · CPC title

• G06F2212/1008

  Correctness of operation, e.g. memory ordering · CPC title