Purging without write-back of cache lines containing spent data

• US 20060026360A1
• Filed: 07/30/2004
• Published: 02/02/2006
• Est. Priority Date: 07/30/2004
• Status: Active Grant

• Current Assignee: Valtrus Innovations Limited (f/k/a Dolya Holdco 9 Limited) (Key Patent Innovations Limited)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Morris, Dale, Schreiber, Robert S.
• Granted Patent: US 8,214,601 B2
• Time in Patent Office: Days
• US Class Current: 711/133
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0891 using clearing, invalidating or resetting means

Abstract

The present invention provides a system with a cache that indicates which, if any, of its sections contain data having spent status. The invention also provides a method for identifying cache sections containing data having spent status and then purging without writing back to main memory a cache line having at least one section containing data having spent status. The invention further provides a program that specifies a cache-line section containing data that is to acquire “spent” status. “Spent” data, herein, is useless modified or unmodified data that was formerly at least potentially useful data when it was written to a cache. “Purging” encompasses both invalidating and overwriting.

Claims

1. A system for providing to a processor copies of data in a memory having memory sections, said system comprising a cache, said cache having plural cache lines of plural cache-line sections each for containing data, each of said cache-line sections representing at most one respective memory section at any given time, said cache further including means for indicating for each of said cache-line sections whether or not it contains data having spent status.

2. A system as recited in claim 1 further comprising a cache manager that purges a cache line without writing back to said memory when all of its sections contain data having spent status.

3. A system as recited in claim 1 further comprising a cache manager that purges a cache line without writing back to said memory when at least one of its sections contains data having spent status and none of its sections contains modified data not having spent status.

4. A system as recited in claim 1 further comprising a cache manager that invalidates without writing back to said memory a cache line when at least one of its sections contains data having spent status and none of its sections contains valid data not having spent status.

5. A system as recited in claim 1 further comprising a cache manager that overwrites a cache line without writing back to said memory when at least one of its sections contains spent data, at least one of its sections contains unmodified data, and none of its sections contains modified data not having spent status.

6. A method comprising:

executing a program of instructions that assigns spent status to data stored in cache-line sections; and

purging without writing back to memory a cache line having at least one section containing data having spent status.

7. A method as recited in claim 6 further comprising flagging cache-line sections that contain spent data to determine when to purge said cache line.

8. A method as recited in claim 6 wherein said purging of a cache line can occur when at least one of its sections contains spent and none of its sections contains unspent modified data.

9. A method as recited in claim 6 wherein said cache-line sections are specified by said program in terms of memory sections they represent

10. A method as recited in claim 9 wherein said program includes an instruction that assigns spent status to data contained in at least one cache-line section.

11. A method as recited in claim 7 wherein said program contains an instruction that assigns a program-controlled condition to data stored in a cache-line section, said condition, when met, causing said data to acquire spent status.

12. A method as recited in claim 11 further comprising indicating that said cache-line section contains data having spent status when said condition is met.

13. A method as recited in claim 11 wherein said instruction is a write instruction causing data to be written to said cache.

14. A method as recited in claim 11 wherein said instruction specifies that data acquire spent status after being read a certain number of times.

15. A method as recited in claim 11 further comprising counting the number of cache-line sections of a cache line that contain spent data to determine when to purge that cache line.

16. A method as recited in claim 6 further wherein said purging involves invalidating a cache line once all of its sections contain data having spent status.

17. Computer readable media comprising a program of instructions that assigns spent status to data stored in a cache-line section.

18. Computer readable media as recited in claim 17 wherein said cache-line section is specified by said program in terms of a memory section it represents.

19. Computer readable media as recited in claim 18 wherein said program includes an instruction that assigns spent status to data stored in one or more cache-line sections, said cache-line sections being specified by said program in terms of the memory sections they represent.

20. Computer readable media as recited in claim 19 wherein said instruction is a mark-as-spent instruction.

21. Computer readable media as recited in claim 19 wherein said instruction is a read-last-time instruction.

22. Computer readable media as recited in claim 18 wherein said program includes an instruction that assigns a program-controlled condition to data contained in a cache-line section, said condition, when met, causing said data to acquire spent status, said cache-line section being specified by said instruction in terms of the memory section it represents.

23. Computer readable media as recited in claim 22 wherein said instruction is a write-as-read-once instruction that specifies that the data written thereby is to be considered spent once it is read in accordance with another instruction.

24. Computer readable media as recited in claim 22 wherein said instruction is a mark-as-read-once instruction that specifies that the data referred to thereby is to be considered spent once it is read in accordance with another instruction.

25. A computer system comprising:

a cache with plural cache lines of plural cache-line sections each for containing data, said cache further including means for indicating for each of said cache lines how many of its sections contain data having spent status, each of said cache-line sections representing at most one respective memory section at any given time; and

a cache manager that purges without writing back to memory a cache line when all of its cache-line sections contain data having spent status.

26. A computer system as recited in claim 25 wherein said cache manager flags cache-line sections containing data having spent status.

27. A computer system as recited in claim 25 wherein said cache manager purges said cache line when at least one of its sections contains data having spent status and none of its sections contains data having unspent modified status.

28. A computer system as recited in claim 25 further comprising an execution unit for executing a program of instructions that assigns a spent status to data stored in a cache-line section.

29. A computer system as recited in claim 28 wherein:

each of said cache-line sections represents at most one respective memory section at any given time; and

said cache-line section being specified by said program in terms of the memory section it represents.

30. A computer system as recited in claim 29 wherein said program includes an instruction that assigns spent status to data contained in a cache-line section, said cache-line section being specified by said instruction in terms of the memory section it represents.

31. A computer system as recited in claim 29 wherein said program includes an instruction that assigns a program-controlled condition to data stored in a cache-line section, said condition, when met, causing said data to acquire spent status, said cache-line section being specified by said instruction in terms of the memory section it represents.

32. A computer system as recited in claim 31 wherein said cache manager indicates that a cache-line section contains data having spent status when said condition is met.

33. A computer system as recited in claim 31 wherein said instruction is a write instruction causing said data to be written to said cache-line section.

34. A computer system as recited in claim 31 wherein said instruction specifies that data is to acquire spent status after being read a specified number of times.