Browse Prior Art Database

Cache Reuse Bit

IP.com Disclosure Number: IPCOM000040358D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Emma, PG: AUTHOR [+8]

Abstract

This invention describes a cache management algorithm that reduces the effect of data or instructions having reference patterns that do not have high reuse probability from displacement of instructions or data that do. When large volumes of data or instructions that are used only while they are in the most recently used (MRU) position in a congruence class are referenced through a cache, instructions and data with reference patterns that result in reuse from other than the MRU position will be displaced from the cache, resulting in more misses and therefore poorer cache performance. This invention provides a bit, the cache reuse bit (CRUB), that in combination with appropriate modifications to the replacement scheme, allows the retention of the reusable data and instructions in the cache.

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Cache Reuse Bit

This invention describes a cache management algorithm that reduces the effect of data or instructions having reference patterns that do not have high reuse probability from displacement of instructions or data that do. When large volumes of data or instructions that are used only while they are in the most recently used (MRU) position in a congruence class are referenced through a cache, instructions and data with reference patterns that result in reuse from other than the MRU position will be displaced from the cache, resulting in more misses and therefore poorer cache performance. This invention provides a bit, the cache reuse bit (CRUB), that in combination with appropriate modifications to the replacement scheme, allows the retention of the reusable data and instructions in the cache. When a line is loaded into the cache on a miss, the CRUB is turned off. It will stay off unless the line is referenced from a non-MRU position in its congruence class. Thus, having the CRUB on for a particular line indicates that the line contains instructions and data that have been reused in the (relatively recent) past and may be expected to be reused again in the future. The replacement scheme of the cache is modified so that on a miss, the least recently used (LRU) line in a congruence class has the CRUB on and the next- to-LRU line has the CRUB off, the next-to-LRU (rather than the LRU) line will be replaced. For caches with other than LRU replacement withi...