Speculative request indicator in request message

Patent metadata

Field	Value
Publication number	US-12332799-B2
Application number	US-202318341217-A
Country	US
Kind code	B2
Filing date	Jun 26, 2023
Priority date	Dec 1, 2022
Publication date	Jun 17, 2025
Grant date	Jun 17, 2025

Abstract

A method and apparatus for a speculative request indicator is described. A method includes providing, for a cache hierarchy, a messaging protocol used for transfer operations among agents in the cache hierarchy, the messaging protocol indicating acceptable cache coherency states for a cache block indicated in a request message and providing, in the messaging protocol for selection by an agent, a speculative request indicator when sending the request message, wherein the speculative request indicator differentiates between a demand request and a speculative request with respect to the cache block.

First claim

What is claimed is:

1. A method comprising:
providing, for a cache hierarchy, a messaging protocol used for transfer operations among agents in the cache hierarchy, the messaging protocol indicating acceptable cache coherency states for a cache block indicated in a request message; and
providing, in the messaging protocol for selection by an agent, a speculative request indicator when sending the request message, wherein the speculative request indicator differentiates between a demand request and a speculative request with respect to the cache block, wherein selection of the speculative request indicator includes at least selecting a bit for an invalid state.

2. The method of claim 1 , the method further comprising:
transmitting, by the agent to another agent, the request message for the cache block, the request message including selection of the speculative request indicator; and
receiving, by the agent from the another agent, a response message with an invalid state responsive to the selection of the speculative request indicator in the request message.

3. The method of claim 1 , wherein selection of the speculative request indicator enables a response from another agent to include an invalid state.

4. The method of claim 1 , wherein selection of the speculative request indicator in the request message for the cache block enables another agent to not service the request message.

5. The method of claim 1 , wherein selection of the speculative request indicator in the request message for the cache block enables another agent to prioritize processing of the request message based on a variety of factors.

6. The method of claim 1 , wherein the messaging protocol includes a first set of request messages with the acceptable cache coherency states, wherein the speculative request indicator is a second set of messages which are a duplicate of the first set of messages, the second set of messages including an invalid state in addition to the acceptable cache coherency states, and wherein the first set of messages are associated with the demand request and the second set of messages are associated with the speculative request.

7. The method of claim 1 , wherein the messaging protocol includes a set of request messages with the acceptable cache coherency states and the speculative request indicator is a flag bit to indicate when a request message being transmitted is for a speculative request.

8. The method of claim 1 , wherein the messaging protocol includes a set of request messages with the acceptable cache coherency states and the speculative request indicator is a mask bit to indicate when a request message being transmitted is for a speculative request.

9. The method of claim 1 , wherein the messaging protocol includes a cache coherency state request vector, wherein a selected bit in the cache coherency state request vector indicates an acceptable cache coherency state for the cache block indicated in the request message.

10. The method of claim 1 , wherein the messaging protocol includes a cache coherency state request vector, wherein a selected bit in the cache coherency state request vector indicates an acceptable cache coherency state for the cache block indicated in the request message, wherein the cache coherency state request vector includes demand configurations and speculative configurations.

11. An apparatus comprising:
one or more processors; and
one or more memories storing instructions that, upon execution by the one or more processors, configure the apparatus to:
provide a messaging protocol for use by agents in a cache hierarchy to enable data operations,

wherein the messaging protocol indicates acceptable cache coherency states for data indicated in a request message,
wherein the messaging protocol provides for selection by an agent, a speculative request indicator when sending the request message, the speculative request indicator differentiating between a demand request and a speculative request with respect to the data, and
wherein selection of the speculative request indicator refers to use of one of speculative configurations of the messaging protocol.

12. The apparatus of claim 11 , wherein the agent configured to:
transmit to another agent, the request message for the data, the request message including selection of the speculative request indicator; and
receive from the another agent, a response message with an invalid state responsive to the selection of the speculative request indicator in the request message.

13. The apparatus of claim 11 , wherein the selection of the speculative request indicator enables a response from another agent to include an invalid state.

14. The apparatus of claim 11 , wherein the selection of the speculative request indicator in the request message for a cache block enables another agent to not service the request message.

15. The apparatus of claim 11 , wherein the selection of the speculative request indicator in the request message for a cache block enables another agent to prioritize processing of the request message based on a variety of factors.

16. The apparatus of claim 11 , wherein the messaging protocol includes a first set of request messages with the acceptable cache coherency states, wherein the speculative request indicator is a second set of messages which are a duplicate of the first set of messages, the second set of messages including an invalid state in addition to the acceptable cache coherency states, and wherein the first set of messages are associated with the demand request and the second set of messages are associated with the speculative request.

17. The apparatus of claim 11 , wherein the messaging protocol includes a set of request messages with the acceptable cache coherency states and the speculative request indicator is a flag bit to indicate when a request message being transmitted is for a speculative request.

18. The apparatus of claim 11 , wherein the messaging protocol includes a set of request messages with the acceptable coherency cache states and the speculative request indicator is a mask bit to indicate when a request message being transmitted is for a speculative request.

19. The apparatus of claim 11 , wherein the messaging protocol includes a cache coherency state request vector, wherein a selected bit in the cache coherency state request vector indicates an acceptable cache coherency state for a cache block indicated in the request message.

20. The apparatus of claim 11 , wherein the messaging protocol includes a cache coherency state request vector, wherein a selected bit in the cache coherency state request vector indicates an acceptable cache coherency state for a cache block indicated in the request message, wherein the cache coherency state request vector includes demand configurations and speculative configurations.

21. A non-transitory computer readable medium storing instructions that, upon execution by one or more processors, cause operations comprising:
providing a messaging protocol for use by agents in a cache hierarchy to enable data operations,
wherein the messaging protocol indicates acceptable cache coherency states for data indicated in a request message and includes a first set of request messages with the acceptable cache coherency states,
wherein the messaging protocol provides for selection by an agent, a speculative request indicator when sending the request message, the speculative request indicator differentiating between a demand request and a speculative request with res

Assignees

• Sifive Inc

Inventors

• Terpstra Wesley Waylon
• Gouldey Eric Andrew
• Klinglesmith Michael
• Cook Henry

Classifications

• G06F12/0811

  with multilevel cache hierarchies · CPC title

• G06F12/0815

  Cache consistency protocols · CPC title

• G06F12/0862 Primary

  with prefetch · CPC title

• G06F12/0813

  with a network or matrix configuration · CPC title

• G06F12/0817

  using directory methods · CPC title