Pre-Fetch Data and Pre-Fetch Data Relative

• US 20090157967A1
• Filed: 12/12/2007
• Published: 06/18/2009
• Est. Priority Date: 12/12/2007
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Greiner, Dan F., Slegel, Timothy J.
• Granted Patent: US 8,122,195 B2
• Time in Patent Office: Days
• US Class Current: 711/125
• CPC Class Codes: G06F 12/0862 with prefetch
• CPC Class Codes: G06F 2212/6028 Prefetching based on hints or prefetch instructions
• CPC Class Codes: G06F 9/30047 Prefetch instructions; cache control instructions
• CPC Class Codes: G06F 9/383 Operand prefetching cache prefetching G06F12/0862
• CPC Class Codes: G06F 9/3832 Value prediction for operands; operand history buffers

Abstract

A prefetch data machine instruction having an M field performs a function on a cache line of data specifying an address of an operand. The operation comprises either prefetching a cache line of data from memory to a cache or reducing the access ownership of store and fetch or fetch only of the cache line in the cache or a combination thereof. The address of the operand is either based on a register value or the program counter value pointing to the prefetch data machine instruction.

Claims

1. A computer program product for executing a prefetch data machine instruction, the computer program product comprising:

a storage medium readable by a processing circuit and storing instructions for execution by the processing circuit of a processor for performing a method comprising;

the processor fetching the prefetch data machine instruction, the prefetch data machine instruction comprising an opcode field, the opcode field specifying the prefetch data machine instruction; and

the processor executing the fetched prefetch data machine instruction adapted to either prefetch data to the cache or change access ownership of a cache line in the cache, the executing comprising;

determining whether to perform a data prefetch cache action or a cache line ownership operation, the data prefetch cache action for prefetching a cache line of data from, memory to the cache, the cache line ownership operation for changing cache access ownership of a line of data in the cache;

determining an address of an operand in memory; and

responsive to determining to perform the cache line ownership operation, performing a determined cache action on a cache line in the cache, the cache line associated with the determined address of the operand, the cache action comprising;

responsive to the determined cache action being a release store access ownership action, changing access ownership of the cache line to a fetch access ownership, the store access ownership indicating that the processor intends to store to the cache line, the fetch access ownership indicating that the processor intends to fetch data from the cache line; and

responsive to the determined cache action being a release fetch access ownership action, releasing access ownership, the released access ownership indicating that the processor does not intend to access to the cache line.

2. The program product according to claim 1, wherein the store access ownership indicates the cache line is not available to other processors, and wherein the fetch access ownership indicates the cadre line may be shared by other processors.

3. The program product according to claim 1, the further comprising:

responsive to the determined cache action being a modified access ownership action, changing access ownership of the cache line to indicate the cache line has been modified; and

responsive to the determined cache action being an owned access ownership action, changing access ownership of the cache line to indicate the cache line is owned.

4. The method according to claim 2, wherein the prefetch data machine instruction further comprises an option field and operand information, wherein the function of the prefetch data machine instruction further comprises:

interpreting the option field to determine whether to perform the data prefetch cache action or the cache line ownership operation;

determining from said operand information, the address of the operand; and

responsive to the determined cache action being a data prefetch action, prefetching said operand into said cache line of said cache.

5. The program product according to claim 4, wherein the cache action comprises:

responsive to the option field being a first value, performing no cache action;

responsive to the option field being a second value, prefetching to the cache, data specified by the operand address for fetch access ownership wherein the cache line access ownership is set as fetch access ownership; and

responsive to the option field being a third value, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership.

6. The program product according to claim 4, wherein the cache action comprises:

responsive to the option field being a fourth value and store access ownership being available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership; and

responsive to the option field being the fourth value and store access ownership being not-available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as fetch access ownership.

7. The program product according to claim 1, wherein the prefetch data machine instruction further comprises a signed immediate field, wherein the address of the operand in memory is related to a memory address of the prefetch instruction being executed, comprising adding a halfword aligned sign extended value of the signed immediate field of the instruction to a program address of the prefetch data instruction being executed to determine the address of the operand in memory.

8. The program product according to claim 1, wherein access ownership is either MESI or MOESI protocol, wherein said cache line is resident in a cache of a processor executing the instruction, said cache action comprising any one of;

changing cache ownership from modified to any one of owned, exclusive, shared or invalid,

changing cache ownership from owned to any one of modified, exclusive, shared or invalid,

changing cache ownership from exclusive to any one of modified, owned, shared or invalid, or

changing cache ownership from shared to any one of modified, owned, exclusive or invalid.

9. The computer program product according to claim 1, further comprising interpreting the prefetch data machine instruction to identify a predetermined software routine for emulating operation of the prefetch data machine instruction;

and

wherein the executing the prefetch data machine instruction comprises executing the predetermined software routine to execute the prefetch data machine instruction.

10. A computer system for executing a prefetch data machine instruction, the system comprising:

a memory;

a cache in communication with the memory; and

a processor in communication with the cache and the memory, the processor comprising an instruction fetching unit for accessing instructions from memory and one or more execution units for executing accessed instructions;

wherein the processor performs a method comprising;

fetching the prefetch data machine instruction, the prefetch data machine instruction comprising an opcode field, the opcode field specifying the prefetch data machine instruction; and

executing the fetched prefetch data machine instruction adapted to either prefetch data to the cache or change access ownership of a cache line in the cache, the executing comprising;

determining whether to perform a data prefetch cache action or a cache line ownership operation, the data prefetch cache action for prefetching a cache line of data from memory to the cache, the cache line ownership operation for changing cache access ownership of a line of data in the cache;

determining an address of an operand in memory; and

responsive to determining to perform the cache line ownership operation, performing a determined cache action on a cache line in the cache, the cache line associated with the determined address of the operand, the cache action comprising;

responsive to the determined cache action being a release store access ownership action, changing access ownership of the cache line to a fetch access ownership, the store access ownership indicating that the processor intends to store to the cache line, the fetch access ownership indicating that the processor intends to fetch data from the cache line; and

responsive to the determined cache action being a release retch access ownership action, releasing access ownership, the released access ownership indicating that the processor does not intend to access to the cache line.

11. The computer system according to claim 10, wherein the store access ownership indicates the cache line is not available to other processors, and wherein the fetch access ownership indicates the cache line may be shared by other processors.

12. The computer system according to claim 10, the further comprising:

responsive to the determined cache action being a modified access ownership action, changing access ownership of the cache line to indicate the cache line has been modified; and

responsive to the determined cache action being an owned access ownership action, changing access ownership of the cache line to indicate the cache line is owned.

13. The computer system according to claim 11, wherein the prefetch data machine instruction further comprises an option field and operand information, wherein the function of the prefetch data machine instruction further comprises:

interpreting the option field to determine whether to perform the data prefetch cache action or the cache line ownership operation;

determining from said operand information, the address of the operand; and

responsive to the determined cache action being a data prefetch action, prefetching said operand into said cache line of said cache.

14. The computer system according to claim 13, wherein the cache action comprises:

responsive to the option field being a first value, performing no cache action;

responsive to the option field being a second value, prefetching to the cache, data specified by the operand address for fetch access ownership wherein the cache line access ownership is set as fetch access ownership; and

responsive to the option field being a third value, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership.

15. The computer system according to claim 13, wherein the cache action comprise:

responsive to the option field being a fourth value and store access ownership being available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership; and

responsive to the option field being the fourth value and store access ownership being not-available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as fetch access ownership

16. The computer system according to claim 10, wherein the prefetch data machine instruction further comprises a signed immediate field, wherein the address of the Operand in memory is related to a memory address of the prefetch instruction being executed, comprising adding a halfword aligned sign extended value of the signed immediate field of the instruction to a program address of the prefetch data instruction being executed to determine the address of the operand in memory.

17. The computer system according to claim 10, wherein access ownership is either MESI or MOESI protocol, wherein said cache line is resident in a cache of a processor executing the instruction, said cache action comprising any one of:

changing cache ownership from modified to any one of owned, exclusive, shared or invalid,

changing cache ownership from owned to any one of modified, exclusive, shared or invalid,

changing cache ownership from exclusive to any one of modified, owned, shared or invalid, or

changing cache ownership from shared to any one of modified, owned, exclusive or invalid.

18. The computer program product according to claim 10, further comprising interpreting the prefetch data machine instruction to identify a predetermined software routine for emulating operation of the prefetch data machine instruction;

and

wherein the executing the prefetch data machine instruction comprises executing the predetermined software routine to execute the prefetch data machine instruction.

19. In a computer system having a processor, wherein the processor is associated with a cache for caching, cache lines of memory information, a method for executing a prefetch data machine instruction of a program, the method comprising:

fetching the prefetch data machine instruction, the prefetch data machine instruction comprising an opcode field, the opcode field specifying the prefetch data machine instruction; and

executing the fetched prefetch data machine instruction adapted to either prefetch data to the cache or change access ownership of a cache line in the cache, the executing comprising;

determining whether to perform a data prefetch cache action or a cache line ownership operation, the data prefetch cache action for prefetching a cache line of data from memory to the cache, the cache line ownership operation for changing cache access ownership of a line of data in the cache;

determining an address of an operand in memory; and

responsive to determining to perform the cache line ownership operation, performing a determined cache action on a cache line in the cache, the cache line associated with the determined address of the operand, the cache action comprising;

responsive to the determined cache action being a release store access ownership action, changing access ownership of the cache line to a fetch access ownership, the store access ownership indicating that the processor intends to store to the cache line, the fetch access ownership indicating that the processor intends to fetch data from the cache line; and

responsive to the determined cache action being a release fetch access ownership action, releasing access ownership, the released access ownership indicating that the processor does not intend to access to the cache line.

20. The method according to claim 19, wherein the store access ownership indicates the cache line is not available to other processors, and wherein the fetch access ownership indicates the cache line may be shared by other processors.

21. The method according to claim 19, wherein the prefetch, data machine instruction further comprises an option field and operand information, wherein the function of the prefetch data machine instruction further comprises:

interpreting the option field to determine whether to perform the data prefetch cache action or the cache line ownership operation;

determining from said operand information, the address of the operand; and

responsive to the determined cache action being a data prefetch action, prefetching said operand into said cache line of said cache.

22. The method according to claim 21, wherein the cache action comprises:

responsive to the option field being a first value, performing no cache action;

responsive to the option field being a second value, prefetching to the cache, data specified by the operand address for fetch access ownership wherein the cache line access ownership is set as fetch access ownership; and

responsive to the option field being a third value, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership.

23. The method according to claim 21, wherein the cache action comprises:

responsive to the option field being a fourth value and store access ownership being available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as store access ownership; and

responsive to the option field being the fourth value and store access ownership being not-available, prefetching to the cache, data specified by the operand address for store access ownership wherein the cache line access ownership is set as fetch access ownership.

24. The method according to claim 19, wherein the prefetch data machine instruction further comprises a signed immediate field, wherein the address of the operand in memory is related to a memory address of the prefetch instruction being executed, comprising adding a halfword aligned sign extended value of the signed immediate field of the instruction to a program address of the prefetch data instruction being executed to determine the address of the operand in memory.

25. The method according to claim 19, further comprising interpreting the prefetch data machine instruction to identify a predetermined software routine for emulating operation of the prefetch data machine instruction;

and

wherein the executing the prefetch data machine instruction comprises executing the predetermined software routine to execute the prefetch data machine instruction.