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Browse Prior Art Database

System for Purging TLB

IP.com Disclosure Number: IPCOM000052724D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Coscarella, AS: AUTHOR [+2]

Abstract

A purge operation on a translation lookaside buffer (TLB) is improved in speed by interleaving TLB accesses for the purge with normal accesses to the TLB. Further improvement in speed is achieved by use of a status word that reduces the search time for an entry that is to be purged.

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System for Purging TLB

A purge operation on a translation lookaside buffer (TLB) is improved in speed by interleaving TLB accesses for the purge with normal accesses to the TLB. Further improvement in speed is achieved by use of a status word that reduces the search time for an entry that is to be purged.

Conventionally, the data store of a processor is accessed with a real address, but programs that contain addressing instructions use logical addresses. A Translation Table which is usually located in main store translates a logical address into a real address. A TLB is a small, fast, store that holds a few of the entries of the Translation Table according to an algorithm that permits most of the accesses to be made to the TLB instead of to the Translation Table.

As storage space is allocated to new user programs and as previously loaded user programs complete, new entries are made in the Translation Table and old entries are removed. When the entry in the Translation Table has also been loaded into the TLB, the entry in the TLB must be removed. The Translation Table has an orderly arrangement of entries, and an entry to be changed can be accessed directly. By contrast, the TLB is an associative store and its entries can be found only by searching the entire TLB.

Purging the TLB is further complicated by the fact that the Translation Table may use indirect addresses. If several user programs are making access to the same storage block in main store, one entry in the Translation Table points to the real main store address and other entries for each user point to this entry. An ""indirect'' bit in the Translation Table identifies these entries. This technique has the advantage that if the storage space is relocated, only one entry in the Translation Table i...