SYSTEM AND METHOD FOR HANDLING DATA REQUESTS

• US 20090150622A1
• Filed: 12/10/2007
• Published: 06/11/2009
• Est. Priority Date: 12/10/2007
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Jenkins, Steven Kenneth, Trombley, Michael Raymond, Mossman, James A., Allen, James Johnson JR.
• Granted Patent: US 7,949,830 B2
• Time in Patent Office: Days
• US Class Current: 711/154
• CPC Class Codes: G06F 12/0806 Multiuser, multiprocessor or multiprocessing cache systems
• CPC Class Codes: G06F 12/0859 with reload from main memory
• CPC Class Codes: G06F 2212/1021 Hit rate improvement
• CPC Class Codes: G06F 2212/507 using speculative control

Abstract

A system and method for handling speculative read requests for a memory controller in a computer system are provided. In one example, a method includes the steps of providing a speculative read threshold corresponding to a selected percentage of the total number of reads that can be speculatively issued, and intermixing demand reads and speculative reads in accordance with the speculative read threshold. In another example, a computer system includes a CPU, a memory controller, memory, a bus connecting the CPU, memory controller and memory, circuitry for providing a speculative read threshold corresponding to a selected percentage of the total number of reads that can be speculatively issued, and circuitry for intermixing demand reads and speculative reads in accordance with the speculative read threshold. In another example, a method includes the steps of providing a speculative dispatch time threshold corresponding to a selected percentage of a period of time required to search a cache of the computer system, and intermixing demand reads and speculative reads in accordance with the speculative dispatch time threshold.

Claims

1. A method for handling speculative read requests for a memory controller in a computer system comprising the steps of:

providing a speculative read threshold corresponding to a selected percentage of the total number of reads to be speculatively issued; and

intermixing demand reads and speculative reads in accordance with the speculative read threshold.

2. The method of claim 1, further comprising the steps of:

monitoring a selected computer system state; and

dynamically adjusting the speculative read threshold based on the selected computer system state.

3. The method of claim 2, further comprising the step of preventing an read request from dispatching as a speculative read request if the percentage of current memory controller resources being used for speculative reads is equal to or greater than the speculative read threshold.

4. The method of claim 3, further comprising the step of preventing the read from dispatching as a speculative read if the memory controller is full.

5. The method of claim 4, further comprising the step of determining the speculative read threshold based on a system read request rate.

6. The method of claim 5, further comprising the step of determining the speculative read threshold based on a percentage of read requests that pass coherency checking and require data from the memory controller.

7. The method of claim 6, further comprising the step of preventing the read from dispatching as a speculative read if the time elapsed from when the memory controller receives the read request to when the memory controller has available resources is greater than a speculative dispatch time threshold.

8. The method of claim 7, further comprising the step of providing the speculative dispatch time threshold as a selected percentage of a period of time required to search a cache of the computer system.

9. The method of claim 8, further comprising the step of preventing the read request from dispatching as a speculative read if the read request is not the youngest available read request.

10. A computer system comprising

a CPU;

a memory controller;

memory;

a bus connecting the CPU, memory controller and memory;

circuitry for providing a speculative read threshold corresponding to a selected percentage of the total number of reads that can be speculatively issued; and

circuitry for intermixing demand reads and speculative reads in accordance with the speculative read threshold.

11. The computer system of claim 10, further comprising:

circuitry for monitoring a selected computer system state; and

circuitry for dynamically adjusting the speculative read threshold based on the selected computer system state.

12. The computer system of claim 11, further comprising circuitry for preventing a read request from dispatching as a speculative read request if the percentage of current memory controller resources being used for speculative reads is equal to or greater than the speculative read threshold.

13. The computer system of claim 12, further comprising circuitry for preventing the read from dispatching as a speculative read if the memory controller is full.

14. The computer system of claim 13, further comprising circuitry for determining the speculative read threshold based on a system read request rate.

15. The computer system of claim 14, further comprising circuitry for determining the speculative read threshold based on a percentage of read requests that pass coherency checking and require data from the memory controller.

16. A method for handling speculative read requests for a memory controller in a computer system comprising the steps of:

providing a speculative dispatch time threshold corresponding to a selected percentage of a period of time required to search a cache of the computer system; and

intermixing demand reads and speculative reads in accordance with the speculative dispatch time threshold.

17. The method of claim 16, further comprising the steps of:

monitoring a selected computer system state; and

dynamically adjusting the speculative dispatch time threshold based on the selected computer system state.

18. The method of claim 17, further comprising the steps of:

providing a speculative read threshold corresponding to a selected percentage of the total number of reads to be speculatively issued; and

intermixing demand reads and speculative reads in accordance with the speculative read threshold.

19. The method of claim 18, further comprising the steps of:

monitoring a selected computer system state; and

dynamically adjusting the speculative read threshold based on the selected computer system state.

20. The method of claim 19, further comprising the step of preventing a read from dispatching as a speculative read if the memory controller is full.