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Partial Store Lines in Store-In-Caches

IP.com Disclosure Number: IPCOM000044536D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+5]

Abstract

This article describes a method of reducing misses in a cache without increasing memory traffic by creating a new line status. A reduction of cache misses in a conventional store-in-cache is achieved by introducing a new line status, called Partial Store. If a line is not resident in a cache or in the cache with read-only (R/O) status, a store to this line is honored by recording it in a blankline (slot) or within the R/O copy with marks to tag the bytes updated. The status of PARTIAL-STORED-UNOWNED is granted to the line, and a request for ownership is made to the System Control Unit (SCU). If ownership is granted, all other cached copies of the line can be made inaccessible and cast-out, if modified.

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Partial Store Lines in Store-In-Caches

This article describes a method of reducing misses in a cache without increasing memory traffic by creating a new line status. A reduction of cache misses in a conventional store-in-cache is achieved by introducing a new line status, called Partial Store. If a line is not resident in a cache or in the cache with read-only (R/O) status, a store to this line is honored by recording it in a blankline (slot) or within the R/O copy with marks to tag the bytes updated. The status of PARTIAL-STORED-UNOWNED is granted to the line, and a request for ownership is made to the System Control Unit (SCU). If ownership is granted, all other cached copies of the line can be made inaccessible and cast-out, if modified. The line status is upgraded to PARTIAL-STORED-OWNED or EXCLUSIVE-MODIFIED and unlimited stores and partial fetches are permitted by the CPU. If ownership is not granted, a normal store-in-cache miss is generated and handled as follows: Associated with the SCU must be an Update Facility which will merge the partial store line with the remainder using the tagged bytes as marks. The granting of ownership and concurrent ownership is architecture and implementation dependent.

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