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Table Lookaside Buffer with Selective Segment Space Invalidation

IP.com Disclosure Number: IPCOM000087098D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Kerrigan, M: AUTHOR [+2]

Abstract

In a virtual storage environment using a table lookaside buffer (TLB) for fast accessing wherein a level of indirect addressing of segment space is allowed, it is generally required to purge the TLB if segment space is written into. The TLB hit ratio is increased by providing for selective invalidation rather than by purging the entire TLB when segment space is written into.

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Table Lookaside Buffer with Selective Segment Space Invalidation

In a virtual storage environment using a table lookaside buffer (TLB) for fast accessing wherein a level of indirect addressing of segment space is allowed, it is generally required to purge the TLB if segment space is written into. The TLB hit ratio is increased by providing for selective invalidation rather than by purging the entire TLB when segment space is written into.

In cases where only the first segment table entry address (STEA) is saved in the TLB regardless of whether a level of indirect addressing (indirection) occurs and where the occurrence of a level of indirection is not routinely remembered, it is necessary to purge the entire TLB if indirection is utilized and if a "write" is executed to segment space. Such purging consumes objectionable amounts of time if "writes" to segment space occur frequently. There is also the problem of many TLB "misses" following each purge because the TLB must be reloaded.

These problems are avoided by (1) saving the information that a direct or an indirect address occurred in the TLB, and (2) saving the intermediate address in the TLB in the case of indirects. It then is unnecessary to purge the TLB all at once since the linkage from the direct to the indirect is saved in the TLB and can be followed to perform selective invalidation. If a write occurs to segment space, at most only one location need be invalidated or, more effectively, it can be updated...