US5623632A — System and method for improving multilevel cache …

Claim 1

Independent Claim 213 words

In a multiprocessor system comprising a plurality of bus devices coupled to a storage device via a bus, wherein said plurality of bus devices have a snoop capability, wherein said plurality of bus device have primary and secondary caches, and wherein said plurality of bus devices utilize a modified MESI data coherency protocol, a method comprising the steps of: reading a data portion from said storage device into one of said plurality of bus devices, wherein said primary cache associated with said one of said plurality of bus devices associates a special exclusive state with said data portion, and wherein said secondary cache associated with said one of said plurality of bus devices associates an exclusive state with said data portion; initiating, by said one of said plurality of bus devices, a write-back operation with respect to said data portion; determining if there are any pending snoop requests in said secondary cache; and changeing said special exclusive state to a modified state in said primary cache if there are no said pending snoop requests in said secondary cache, wherein said special exclusive state indicates that said data portion is held in said primary cache in a shared state and indicates said data portion is held in said secondary cache in an exclusive state.

Claim 2

Dependent Claim 213 words

In a multiprocessor system comprising a plurality of bus devices coupled to a storage device via a bus, wherein said plurality of bus devices have a snoop capability, wherein said plurality of bus device have primary and secondary caches, and wherein said plurality of bus devices utilize a modified MESI data coherency protocol, a method comprising the steps of: reading a data portion from said storage device into one of said plurality of bus devices, wherein said primary cache associated with said one of said plurality of bus devices associates a special exclusive state with said data portion, and wherein said secondary cache associated with said one of said plurality of bus devices associates an exclusive state with said data portion; initiating, by said one of said plurality of bus devices, a write-back operation with respect to said data portion; determining if there are any pending snoop requests in said secondary cache; and changeing said special exclusive state to a modified state in said primary cache if there are no said pending snoop requests in said secondary cache, wherein said special exclusive state indicates that said data portion is held in said primary cache in a shared state and indicates said data portion is held in said secondary cache in an exclusive state.

Claim 3

Dependent Claim 53 words

The method as recited in claim 1, further comprising the steps of: if there is a pending snoop request in said secondary cache, comparing addresses of said pending snoop request and said data portion; and changing said special exclusive state to said modified state in said primary cache if said addresses are different.

Claim 4

Dependent Claim 25 words

The method as recited in claim 1, further comprising the step of: changing said exclusive state associated with said secondary cache to said modified state.

Claim 5

Dependent Claim 30 words

The method as recited in claim 1, further comprising the step of: modifying, by said one of said plurality of bus devices, said data portion prior to said write-back operation.

Claim 6

Dependent Claim 49 words

The method as recited in claim 1, further comprising the step of: initiating a DCLAIM request from said primary cache to said secondary cache in response to said step of initiating, by said one of said plurality of bus devices, said write-back operation with respect to said data portion.

Claim 7

Dependent Claim 20 words

The method as recited in claim 5, wherein said changing step further comprises the step of approving said DCLAIM request.

Claim 8

Dependent Claim 45 words

The method as recited in claim 5, further comprising the steps of: rejecting said DCLAIM request if an address of said pending snoop request matches an address of said data portion; and initiating, by said primary cache, a gaining of ownership of said data portion.

Claim 9

Dependent Claim 42 words

The method as recited in claim 1, wherein said special exclusive state indicates to said secondary cache that said secondary cache does not need to make a determination whether the data portion is held in said secondary cache in said exclusive state.

Claim 10

Dependent Claim 168 words

A multiprocessor system comprising: system memory; a memory controller coupled to said system memory; a plurality of processors; a system bus coupling said plurality of processors to said memory controller; primary and secondary caches associated with one of said plurality of processors, wherein said secondary cache implements a MESI protocol, and wherein said primary cache implements a modified MESI protocol comprising a special exclusive state; means for initiating, by said one of said plurality of processors, a write-back operation with respect to a data portion; cache control logic circuitry for determining if there are any pending snoop requests in said secondary cache; and cache control logic circuitry for changing said special exclusive state in said primary cache to a modified state if there are no said pending loop requests in said secondary cache, wherein said special exclusive state indicates that said data portion is held in said primary cache in a shared state and that said data portion is held in said secondary cache in an exclusive state.

Claim 11

Dependent Claim 168 words

A multiprocessor system comprising: system memory; a memory controller coupled to said system memory; a plurality of processors; a system bus coupling said plurality of processors to said memory controller; primary and secondary caches associated with one of said plurality of processors, wherein said secondary cache implements a MESI protocol, and wherein said primary cache implements a modified MESI protocol comprising a special exclusive state; means for initiating, by said one of said plurality of processors, a write-back operation with respect to a data portion; cache control logic circuitry for determining if there are any pending snoop requests in said secondary cache; and cache control logic circuitry for changing said special exclusive state in said primary cache to a modified state if there are no said pending loop requests in said secondary cache, wherein said special exclusive state indicates that said data portion is held in said primary cache in a shared state and that said data portion is held in said secondary cache in an exclusive state.

Claim 12

Dependent Claim 60 words

The system as recited in claim 9, further comprising: cache control logic circuitry for comparing addresses of said pending snoop requests and said data portion if there is a pending snoop request in said secondary cache; and cache control logic circuitry for changing said special exclusive state to a modified state in said primary cache if said addresses are different.

Claim 13

Dependent Claim 50 words

The system as recited in claim 10, further comprising: cache control logic circuitry for initiating a DCLAIM request from said primary cache to said secondary cache in response to said step of initiating, by said one of said plurality of processors, a write-back operation with respect to said data portion.

Claim 14

Dependent Claim 27 words

The system as recited in claim 9, further comprising: cache control logic circuitry for changing said exclusive state associated with said secondary cache to a modified state.

Claim 15

Dependent Claim 28 words

The system as recited in claim 9, further comprising: means for modifying, by said one of said plurality of processors, said data portion prior to said write-back operation.

Claim 16

Dependent Claim 49 words

The system as recited in claim 9, further comprising: cache control logic circuitry for rejecting said DCLAIM request if an address of said pending snoop request matches an address of said data portion; and means for initiating, by said primary cache, a gaining of ownership of said data portion.

Claim 17

Dependent Claim 42 words

The system as recited in claim 9, wherein said special exclusive state indicates to said secondary cache that said secondary cache does not need to make a determination whether the data portion is held in said secondary cache in an exclusive state.

Claim 18

Dependent Claim 184 words

A multiprocessor system comprising: system memory; a memory controller coupled to said system memory; a plurality of processors; a system bus coupling said plurality of processors to said memory controller: first and second caches associated with one of said plurality of processors, wherein said first cache is a write-through cache and said second cache is a write-back cache, wherein said second cache implements a MESI protocol, and wherein said first cache implements a modified MESI protocol comprising a special exclusive state; means for initiating, by said one of said plurality of processors, a write-back operation with respect to a data portion; cache control logic circuitry for determining if there are any pending snoop requests in said second cache; and cache control logic circuitry for changing said special exclusive state in said first cache to a modified state if there are no said pending snoop requests in said second cache, wherein said special exclusive state indicates that data said portion is held in said first cache in a shared state and that said data portion is held in said second cache in an exclusive state.

Claim 19

Dependent Claim 184 words

A multiprocessor system comprising: system memory; a memory controller coupled to said system memory; a plurality of processors; a system bus coupling said plurality of processors to said memory controller: first and second caches associated with one of said plurality of processors, wherein said first cache is a write-through cache and said second cache is a write-back cache, wherein said second cache implements a MESI protocol, and wherein said first cache implements a modified MESI protocol comprising a special exclusive state; means for initiating, by said one of said plurality of processors, a write-back operation with respect to a data portion; cache control logic circuitry for determining if there are any pending snoop requests in said second cache; and cache control logic circuitry for changing said special exclusive state in said first cache to a modified state if there are no said pending snoop requests in said second cache, wherein said special exclusive state indicates that data said portion is held in said first cache in a shared state and that said data portion is held in said second cache in an exclusive state.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	2000-04-21	2000-10-21	2001-04-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2004-04-21	2004-10-21	2005-04-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2008-04-21	2008-10-21	2009-04-22	$7700.00	Window Closed / Lapsed

System and method for improving multilevel cache performance in a multiprocessing system

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