Cache system

• US 20030196041A1
• Filed: 05/23/2003
• Published: 10/16/2003
• Est. Priority Date: 01/30/1997
• Status: Active Grant

• Current Assignee: Microelectronic Innovations LLC
• Original Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Inventors: May, David, Sturges, Andrew Craig
• Granted Patent: US 6,871,266 B2
• Time in Patent Office: Days
• US Class Current: 711/129
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0842 for multiprocessing or multitasking
• CPC Class Codes: G06F 12/0848 Partitioned cache, e.g. separate instruction and operand caches
• CPC Class Codes: G06F 12/0864 using pseudo-associative means, e.g. set-associative or hashing
• CPC Class Codes: G06F 12/1045 associated with a data cache

Abstract

A cache system is provided which includes a cache memory and a cache refill mechanism which allocates one or more of a set of cache partitions in the cache memory to an item in dependence on the address of the item in main memory. This is achieved in one of the described embodiments by including with the address of an item a set of partition selector bits which allow a partition mask to be generated to identify into which cache partition the item may be loaded.

Claims

1. A cache system for operating between a processor and a main memory of a computer, the cache system comprising:

a cache memory having a set of cache partitions, each cache partition comprising a plurality of addressable storage locations for holding items fetched from said main memory for use by the processor;

a cache refill mechanism arranged to fetch an item from the main memory and to load said item into the cache memory at one of said addressable storage locations; and

a cache partition mask generator which generates from a partition selector associated with the address of an item to be cached a multi-bit partition mask identifying into which cache partition the item may be loaded so that the cache refill mechanism is operable to allocate to each said item fetched from the main memory one of said cache partitions in dependence on the address of said item in the main memory.

2. A cache system according to claim 1, wherein the partition selector defines the number of cache partitions into which the cache memory is divisible.

3. A cache system according to claim 2, wherein the partition selector is a bit sequence including a guard bit the position of which in the bit sequence defines the number of cache partitions into which the cache memory is divisible.

4. A cache system according to claim 2 or 3, wherein the partition selector includes a partition index bit sequence which defines the location of the cache partition into which the item is to be loaded.

5. A cache system according to any preceding claim, wherein each address in main memory comprises a page number and an offset.

6. A cache system according to any of claims 1 to 5, wherein the processor issues addresses comprising a virtual page number and an offset and wherein the system comprises a translation look-aside buffer for translating the virtual page number to a real page number for accessing the main memory.

7. A cache system according to claim 5 or 6, wherein the offset of the item'"'"'s address is used with the partition mask to identify the addressable storage location within the cache partition into which the item is to be located.

8. A cache system according to any preceding claim, wherein one or more cache partitions is allocated to a page in main memory.

9. A cache system according to any preceding claim, comprising a cache access circuit which accesses items from the cache memory according to the addresses in main memory of said items and regardless of the cache partition in which the item is held in the cache memory.

10. A method of operating a cache memory arranged between a processor and a main memory of a computer, wherein, when the processor requests an item from main memory using an address in main memory for said item and that item is not held in the cache memory, said item is fetched from the main memory and loaded into one of a plurality of addressable storage locations in the cache memory, the addressable storage locations being arranged as a set of cache partitions and wherein each address includes a multi-bit partition selector identifying into which cache partition the item may be loaded so that one of said cache partitions is allocated to said item in dependence on the address of said item in main memory.

11. A method according to claim 10, wherein each address in main memory comprises a page number and a line-in-page number and wherein a plurality of processes are held in the main memory, each process including one or more sequence of instructions held at addresses in main memory with a common page number.

12. A method according to claim 11, wherein one of said cache partitions is allocated to a process by associating said one cache partition with page numbers of that process in the main memory.

13. A method according to claim 10, 11 or 12, wherein the number of addressable storage locations in each cache partition is alterable.

14. A method according to claim 10, 11, 12 or 13, wherein the association of cache partitions to page numbers is alterable while a process using these page numbers is being run by the processor.

15. A cache system for operating between a processor and a main memory of a computer, the cache system comprising:

a cache memory having a set of cache partitions, each cache partition comprising a plurality of addressable storage locations for holding items fetched from said main memory for use by the processor; and

a cache refill mechanism arranged to fetch an item from the main memory and to load said item into the cache memory at one of said addressable storage locations, wherein the cache refill mechanism is operable to allocate to each said item fetched from the main memory one or more of said cache partitions in dependence on the address of said item in the main memory.