Prefetch threshold for cache restoration

Patent metadata

Field	Value
Publication number	US-2016357676-A1
Application number	US-201514733168-A
Country	US
Kind code	A1
Filing date	Jun 8, 2015
Priority date	Jun 8, 2015
Publication date	Dec 8, 2016
Grant date	—

Abstract

Embodiments relate to a prefetch threshold for cache restoration. An aspect includes determining, based on a task switch from an outgoing task to a current task in a processor, a prefetch threshold for a next task, the prefetch threshold corresponding to an expected runtime of the current task and an amount of time required to prefetch data for the next task. Another aspect includes starting prefetching for the next task while the current task is executing based on the prefetch threshold.

First claim

What is claimed is:

1 . A computer implemented method for a prefetch threshold for cache restoration, the method comprising:
determining, based on a task switch from an outgoing task to a current task in a processor, a prefetch threshold for a next task, the prefetch threshold corresponding to an expected runtime of the current task and an amount of time required to prefetch data for the next task; and starting prefetching for the next task while the current task is executing based on the prefetch threshold.

2 . The method of claim 1 , further comprising, based on the task switch:
determining a most recent runtime for the outgoing task; and determining an updated expected runtime for the outgoing task based on the most recent runtime of the outgoing task.

3 . The method of claim 2 , wherein the updated expected runtime is the most recent runtime.

4 . The method of claim 2 , wherein the updated expected runtime comprises an average of the most recent runtime and a historical runtime value of the outgoing task.

5 . The method of claim 4 , wherein the historical runtime value comprises a value taken from a runtime value field in an entry corresponding to the outgoing task in an operating system (OS) task queue; and further comprising:
inserting the updated expected runtime for the outgoing task into the runtime value field in the entry corresponding to the outgoing task in the operating system (OS) task queue.

6 . The method of claim 1 , wherein the expected runtime of the current task is determined based on a runtime value field in an entry corresponding to the current task in the OS task queue, and wherein the amount of time required to prefetch data for the next task is determined based on a cache restoration data field in an entry corresponding to the next task in an OS task queue and an amount of time required per prefetch.

7 . The method of claim 1 , wherein the prefetch threshold further corresponds to a slowdown factor corresponding to an amount of slowdown expected in the execution of the current task due to performing the prefetching for the next task.

8 . The method of claim 1 , wherein the prefetch threshold is stored in a prefetch register, and wherein the prefetching is started for the next task based on the prefetch threshold that is stored in the prefetch register being equal to a task switch timer of the processor.

9 . A computer program product for implementing a prefetch threshold for cache restoration, the computer program product comprising:
a computer readable storage medium having program instructions embodied therewith, the program instructions readable by a processing circuit to cause the processing circuit to perform a method comprising: determining, based on a task switch from an outgoing task to a current task in a processor, a prefetch threshold for a next task, the prefetch threshold corresponding to an expected runtime of the current task and an amount of time required to prefetch data for the next task; and starting prefetching for the next task while the current task is executing based on the prefetch threshold.

10 . The computer program product of claim 9 , further comprising, based on the task switch:
determining a most recent runtime for the outgoing task; and determining an updated expected runtime for the outgoing task based on the most recent runtime of the outgoing task.

11 . The computer program product of claim 10 , wherein the updated expected runtime is the most recent runtime.

12 . The computer program product of claim 10 , wherein the updated expected runtime comprises an average of the most recent runtime and a historical runtime value of the outgoing task.

13 . The computer program product of claim 12 , wherein the historical runtime value comprises a value taken from a runtime value field in an entry corresponding to the outgoing task in an operating system (OS) task queue; and further comprising:
inserting the updated expected runtime for the outgoing task into the runtime value field in the entry corresponding to the outgoing task in the operating system (OS) task queue.

14 . The computer program product of claim 9 , wherein the expected runtime of the current task is determined based on a runtime value field in an entry corresponding to the current task in the OS task queue, and wherein the amount of time required to prefetch data for the next task is determined based on a cache restoration data field in an entry corresponding to the next task in an OS task queue and an amount of time required per prefetch.

15 . The computer program product of claim 9 , wherein the prefetch threshold further corresponds to a slowdown factor corresponding to an amount of slowdown expected in the execution of the current task due to performing the prefetching for the next task.

16 . A computer system for a prefetch threshold for cache restoration, the system comprising:
a memory; and a processor, communicatively coupled to said memory, the computer system configured to perform a method comprising: determining, based on a task switch from an outgoing task to a current task in a processor, a prefetch threshold for a next task, the prefetch threshold corresponding to an expected runtime of the current task and an amount of time required to prefetch data for the next task; and starting prefetching for the next task while the current task is executing based on the prefetch threshold.

17 . The system of claim 16 , further comprising, based on the task switch:
determining a most recent runtime for the outgoing task; and determining an updated expected runtime for the outgoing task based on the most recent runtime of the outgoing task.

18 . The system of claim 17 , wherein the updated expected runtime comprises an average of the most recent runtime and a historical runtime value of the outgoing task.

19 . The system of claim 18 , wherein the historical runtime value comprises a value taken from a runtime value field in an entry corresponding to the outgoing task in an operating system (OS) task queue; and further comprising:
inserting the updated expected runtime for the outgoing task into the runtime value field in the entry corresponding to the outgoing task in the operating system (OS) task queue.

20 . The system of claim 16 , wherein the expected runtime of the current task is determined based on a runtime value field in an entry corresponding to the current task in the OS task queue, and wherein the amount of time required to prefetch data for the next task is determined based on a cache restoration data field in an entry corresponding to the next task in an OS task queue and an amount of time required per prefetch.

Assignees

• IBM

Inventors

• Cain Iii Harold W
• Daly David M
• Prasky Brian R
• Srinivasan Vijayalakshmi

Classifications

• G06F9/48

  Program initiating; Program switching, e.g. by interrupt · CPC title

• G06F9/4887

  involving deadlines, e.g. rate based, periodic · CPC title

• G06F2212/602

  Details relating to cache prefetching · CPC title

• G06F12/0862 Primary

  with prefetch · CPC title