Method for generating prefetch instruction with a field specifying type of information and location for it such as an instruction cache or data cache

• US 5,796,971 A
• Filed: 08/22/1997
• Issued: 08/18/1998
• Est. Priority Date: 07/07/1995
• Status: Expired due to Term

• Current Assignee: David R. Emberson
• Original Assignee: David R. Emberson
• Inventors: Emberson, David R.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): PATEL, GAUTAM
• Application Number:
  US08/918,707
• Time in Patent Office: 361 Days
• Field of Search: 395/383, 395/450, 395/449, 395/468
• US Class Current: 712/207
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 12/1027 using associative or pseudo-associative address translation means, e.g. translation look-aside buffer [TLB]
• CPC Class Codes: G06F 2212/6028 Prefetching based on hints or prefetch instructions
• CPC Class Codes: G06F 9/3802 Instruction prefetching
• CPC Class Codes: G06F 9/383 Operand prefetching cache prefetching G06F12/0862

Abstract

Disclosed is a method and system for providing for the prefetching of data or instructions. A prefetch instruction which is in an instruction stream is processed by memory management unit (MMU) where prefetch cache control information is placed as part of the already existing prefetch instruction. Once processed by the MMU, the prefetch instruction thus contains binary fields allowing the operating system or runtime software to control cache prefetching by assigning values to the binary fields which provide the optimal cache set location and the optimal amount of data to be prefetched and thus reduces thrashing.

Claims

1. A method for use by a computer which has a main memory for maintaining stored information which is either data or instructions and a cache memory including a data cache and an instruction cache, said method for enhancing an already existing prefetch instruction for use by a prefetch unit, comprising the steps of:

receiving said already existing prefetch instruction;

adding a dynamically adjustable unfilled instruction/data field to form an annexed prefetch instruction;

receiving said annexed prefetch instruction including said dynamically adjustable unfilled instruction/data field; and

filling said dynamically adjustable unfilled instruction/data field with a prefetch type value which indicates whether said stored information is instructions or data, such indicating whether to store said information in said instruction cache or in said data cache to generate an enhanced prefetch instruction.

2. A method as recited in claim 1, said method further comprising the steps of:

adding a dynamically adjustable unfilled size field to further form said annexed prefetch instruction;

filling said dynamically adjustable unfilled size field with a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache memory.

3. A method as recited in claim 1 wherein said instruction cache includes at least two cache sets and wherein said data cache includes at least two cache sets, said method further comprising the steps of:

adding a dynamically adjustable unfilled set field to further form said annexed prefetch instruction;

filling said dynamically adjustable unfilled cache set field with a prefetch type value to indicate which of said cache sets to store information retrieved from said main memory.

4. A method as recited in claim 1 wherein said computer runs an operating system and wherein said operating system provides said prefetch type value which is inserted into said instruction/data field.

5. A method as recited in claim 1 wherein said computer runs runtime software and wherein said runtime software provides said prefetch type value which is inserted into said instruction/data field.

6. A method for use by a computer which has a main memory for maintaining stored information and a cache memory, said method for enhancing an already existing prefetch instruction for use by a prefetch unit, comprising the steps of:

receiving said already existing prefetch instruction;

adding a dynamically adjustable unfilled size field to form an annexed prefetch instruction;

receiving said annexed prefetch instruction;

filling said dynamically adjustable unfilled size filed with a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache to generate an enhanced prefetch instruction.

7. A method as recited in claim 6 wherein said cache memory includes an instruction cache and a data cache and wherein said initial prefetch instruction further includes an unfilled instruction/data field, said method further comprising the steps of:

adding a dynamically adjustable unfilled instruction/data field to further form said annexed prefetch instruction;

filling said dynamically adjustable unfilled instruction/data field with a prefetch type value which indicates whether said information is instructions or data, such indicating whether to store said information in said instruction cache or said data cache.

8. A method as recited in claim 6 wherein said instruction cache includes at least two cache sets and wherein said data cache includes at least two cache sets, said method further comprising the steps of:

adding a dynamically adjustable unfilled cache set field to further form said annexed prefetch instruction;

filling said dynamically adjustable unfilled cache set field with a prefetch type value which indicates which of said cache sets to store said information retrieved from said main memory.

9. A method as recited in claim 6 wherein said computer runs an operating system and wherein said operating system provides said prefetch type value which is inserted into said instruction/data field.

10. A method as recited in claim 6 wherein said computer runs runtime software and wherein said runtime software provides said prefetch type value which is inserted into said instruction/data field.

11. A method for use by a computer which has a main memory for maintaining stored information and a cache memory including at least two cache sets, said method for enhancing an already existing prefetch instruction for use by a prefetch unit, comprising the steps of:

receiving said already existing prefetch instruction;

adding a dynamically adjustable unfilled cache set field to form an annexed prefetch instruction;

receiving an annexed prefetch instruction including an unfilled cache set field; and

filling said unfilled cache set field with a prefetch type value to indicate which of said at least two cache sets to store information retrieved from said main memory to generate an enhanced prefetch instruction.

12. A method as recited in claim 11 said method further comprising the steps of:

adding a dynamically adjustable unfilled size field to further form said annexed prefetch instruction; and

filling said dynamically adjustable unfilled size field with a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache memory.

13. A method as recited in claim 11 wherein said information is either instructions or data and wherein said cache memory includes an instruction cache and a data cache said method further comprising the steps of:

adding a dynamically adjustable unfilled instruction/data field to further form said annexed prefetch instruction; and

filling said dynamically adjustable unfilled instruction/data field with a prefetch type value to indicate whether said information is instructions or data, such indicating whether to store said information in said instruction cache or said data cache.

14. A method as recited in claim 11 wherein said computer runs an operating system and wherein said operating system provides said prefetch type value which is inserted into said cache set field.

15. A method as recited in claim 11 wherein said computer runs runtime software and wherein said runtime software provides said prefetch type value which is inserted into said cache set field.

16. A method for use by a computer which has a memory management unit, a main memory for maintaining stored information which is either data or instructions and a cache memory including a data cache and an instruction cache, said method for generating an enhanced prefetch instruction, comprising the steps of:

receiving an initial prefetch instruction; and

said memory management unit enhancing said initial prefetch instruction to generate an enhanced prefetch instruction as output which includes a dynamically adjustable unfilled instruction/data field which is subsequently filled with a prefetch type value which indicates whether said stored information is instructions or data such indicating whether to store said information in said instruction cache or said data cache.

17. A method as recited in claim 16 further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable size field including a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache memory.

18. A method as recited in claim 16 wherein said instruction cache includes at least two cache sets and wherein said data cache includes at least two cache sets, said method further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable cache set field including a prefetch type value which indicates which of said cache sets to store information retrieved from said main memory.

19. A method for use by a computer which has a memory management unit, a main memory for maintaining stored information and a cache memory, said method for providing an enhanced prefetch instruction, comprising the steps of:

receiving an initial prefetch instruction; and

said memory management unit enhancing said initial prefetch instruction to generate an enhanced prefetch instruction as output which includes a dynamically adjustable unfilled size field which is subsequently filled with a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache memory.

20. A method as recited in claim 19 wherein said cache memory includes an instruction cache and a data cache, said method further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable instruction/data field including a prefetch type value which indicates whether said information is instructions or data and thus to indicate whether to store said information in said instruction cache or said data cache.

21. A method as recited in claim 20 wherein said instruction cache includes at least two cache sets and wherein said data cache includes at least two cache sets, said method further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable cache set field including a prefetch type value which indicates which of said cache sets to store said information retrieved from said main memory.

22. A method for use by a computer which has a memory management unit, a main memory for maintaining stored information and a cache memory including at least two cache sets, said method for providing an enhanced prefetch instruction, comprising the steps of:

receiving an initial prefetch instruction; and

said memory management unit enhancing said initial prefetch instruction to generate an enhanced prefetch instruction as output which includes a dynamically adjustable unfilled cache set field which is subsequently filled with a prefetch type value which indicates which of said at least two dynamically adjustable cache sets to store information retrieved from said main memory.

23. A method as recited in claim 22 further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable size field including a prefetch type value which indicates how much information to retrieve from said main memory and store in said cache memory.

24. A method as recited in claim 22 wherein said information is either instructions or data and wherein said cache memory includes an instruction cache and a data cache, said method further comprising the step of:

said memory management unit further enhancing said initial prefetch instruction to include a dynamically adjustable instruction/data field including a prefetch type value which indicates whether said information is instructions or data and thus to indicate whether to store said information in said instruction cache or said data cache.

25. A computer system including a CPU, a main memory for maintaining stored information which is either data or instructions, a cache memory including a data cache and an instruction cache, wherein said CPU is configured to execute an instruction stream which includes a prefetch instruction configured to effect the prefetch of information stored in said main memory which will be required by said CPU, said system for providing an enhanced prefetch instruction, comprising:

a memory management unit configured to receive said initial prefetch instruction and to generate as output an enhanced prefetch instruction which includes a dynamically adjustable unfilled instruction/data field which is subsequently filled with a prefetch type value which indicates whether the information required by said CPU which is stored in said main memory is instructions or data, and thus indicates whether to store said information in said instruction cache or said data cache; and

a prefetch unit configured to execute said enhanced prefetch instruction so that said information is retrieved from said main memory and is stored in either said instruction cache or said data cache in accordance with said prefetch type value included in said dynamically adjustable instruction/data field.

26. A system as recited in claim 25 wherein said enhanced prefetch instruction generated by said memory management unit further includes a dynamically adjustable size field including a prefetch type value configured to indicate how much information to retrieve from said main memory and store in said cache memory.

27. A system as recited in claim 25 wherein said instruction cache includes at least two instruction cache sets and wherein said enhanced prefetch instruction generated by said memory management unit further includes a dynamically adjustable instruction cache set field including a prefetch type value configured to indicate which of said instruction cache sets to store information retrieved from said main memory.

28. A system as recited in claim 25 wherein said data cache includes at least two data cache sets and wherein said enhanced prefetch instruction generated by said memory management unit further includes a dynamically adjustable data cache set field including a prefetch type value configured to indicate which of said data cache sets to store information retrieved from said main memory.

29. A prefetch enhancement device operable in conjunction with a computer having a CPU, a main memory for maintaining stored information which is either data or instructions, wherein said CPU is configured to execute an instruction stream which includes a prefetch instruction configured to effect the prefetch of information stored in said main memory which will be required by said CPU, said device comprising:

a memory management unit configured to receive a prefetch instruction and to generate as output an enhanced prefetch instruction having a dynamically adjustable unfilled instruction/data field which is subsequently filled with a prefetch type value which indicates whether the information required by said CPU which is stored in said main memory is instructions or data, and thus indicates whether to store said information in said instruction cache or said data cache; and

a prefetch unit configured to execute said enhanced prefetch instruction so that said information is retrieved from said main memory and is stored in either said instruction cache or said data cache in accordance with said prefetch type value included in said dynamically adjustable instruction/data field.

30. A device as recited in claim 29 wherein said enhanced instruction prefetch generated by said memory management unit further includes a dynamically adjustable size field including a prefetch type value configured to indicate how much information to retrieve from said main memory and store in said cache memory.

31. A device as recited in claim 29 wherein said instruction cache includes at least two instruction cache sets and wherein said enhanced prefetch instruction generated by said memory management unit further includes a dynamically adjustable instruction cache set field including a prefetch type value configured to indicate which of said instruction cache sets to store information retrieved from said main memory.

32. A device as recited in claim 29 wherein said data cache includes at least two data cache sets and wherein said enhanced prefetch instruction generated by said memory management unit further includes a dynamically adjustable data cache set field including a prefetch type value configured to indicate which of said data cache sets to store information retrieved from said main memory.