Data cache with prediction hints for cache hits

Patent metadata

Field	Value
Publication number	US-11620229-B2
Application number	US-202016797476-A
Country	US
Kind code	B2
Filing date	Feb 21, 2020
Priority date	Feb 21, 2020
Publication date	Apr 4, 2023
Grant date	Apr 4, 2023

Abstract

Described is a data cache with prediction hints for a cache hit. The data cache includes a plurality of cache lines, where a cache line includes a data field, a tag field, and a prediction hint field. The prediction hint field is configured to store a prediction hint which directs alternate behavior for a cache hit against the cache line. The prediction hint field is integrated with the tag field or is integrated with a way predictor field.

First claim

What is claimed is:

1. A data cache comprising:
a plurality of cache lines, at least one cache line comprising:
a data field;
a tag field;
a way predictor field; and
a prediction hint field, wherein the prediction hint field stores an alternate instruction behavior and an instruction of a pre-determined instruction type, wherein the alternate instruction behavior is performed responsive to a determination that an issued instruction matches the instruction.

2. The data cache of claim 1 , wherein the prediction hint field is integrated with the tag field.

3. The data cache of claim 1 ,
wherein the prediction hint field is integrated with the way predictor field.

4. The data cache of claim 1 , wherein the data cache is a LI data cache.

5. The data cache of claim 1 , wherein the pre-determined instruction type is an instruction which is repeatedly being re-executed.

6. The data cache of claim 1 , wherein the at least one cache line is a subset of the plurality of cache lines.

7. The data cache of claim 1 , wherein the alternate instruction behavior is a disable load data return in response to unknown Read-After-Write hazard.

8. The data cache of claim 1 , wherein the alternate instruction behavior is a speculative store bypass disable.

9. The data cache of claim 1 , wherein certain prediction hint fields are unpopulated.

10. A data cache comprising:
a data array;
a tag array;
a way predictor field; and
a prediction hint field, wherein the prediction hint field stores alternate instruction behavior and an instruction of a pre-determined instruction type, wherein the alternate instruction behavior is performed responsive to a determination that an issued instruction matches the instruction.

11. The data cache of claim 10 , wherein each entry of the tag array has an integrated prediction hint field.

12. The data cache of claim 11 , wherein certain prediction hint fields are unpopulated.

13. The data cache of claim 10 ,
wherein each entry in the way predictor array has an integrated prediction hint field.

14. The data cache of claim 10 , wherein the alternate instruction behavior is a disable load data return in response to unknown Read-After-Write hazard.

15. The data cache of claim 10 , wherein the alternate instruction behavior is a speculative store bypass disable.

16. The data cache of claim 10 , wherein the alternate instruction behavior is an alternate instruction.

17. A method for providing prediction hints using a data cache, the method comprising:
storing alternate instruction behavior and an instruction of a pre-determined instruction type in a prediction hint element for certain cache lines in a way predictor of the data cache;
comparing an issued instruction to the instruction stored in the prediction hint element; and
performing the alternate instruction behavior responsive to a determination that an issued instruction matches the instruction.

18. The method of claim 17 , wherein the alternate instruction behavior is a disable load data return in response to unknown Read-After-Write hazard.

19. The method of claim 18 , wherein the alternate instruction behavior is a speculative store bypass disable.

20. The method of claim 19 ,
wherein the pre-determined instruction type is an instruction which is repeatedly being re-executed.

Assignees

• Sifive Inc

Inventors

• Ingalls John
• Smith Josh

Classifications

• G06F2212/603

  of operating mode, e.g. cache mode or local memory mode · CPC title

• G06F2212/6028

  Prefetching based on hints or prefetch instructions · CPC title

• G06F12/0888 Primary

  using selective caching, e.g. bypass · CPC title

• G06F12/0862 Primary

  with prefetch · CPC title