Browse Prior Art Database

Mechanism for Avoiding Unnecessary Cross Interrogates

IP.com Disclosure Number: IPCOM000045733D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Hoevel, LW: AUTHOR [+2]

Abstract

It is clear that cross interrogates (and cross invalidates) are not logically required to fetch read-only data and program code. It is suggested that these logical features be exploited to improve multi-processor (MP) and attached processor (AP) performance.

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Mechanism for Avoiding Unnecessary Cross Interrogates

It is clear that cross interrogates (and cross invalidates) are not logically required to fetch read-only data and program code. It is suggested that these logical features be exploited to improve multi-processor (MP) and attached processor (AP) performance.

Unfortunately, there is no mechanism or convention that guarantees the entire content of any given cache line is read-only. Indeed, no attempt is currently made to maximize the number of read-only lines by excluding read-write data from areas of read-only data and program code.

It is proposed that such an ef fort be made, both during coding and by the link-loaded for proprietary code. The read-only status of a line would be indicated in some manner -- either by extra 'tag' bits in memory, or by being placed in a 'read-only' area of storage. This strategy suggests the natural separation of read-write data from the (re-entrant) code that manipulates it. 'Read-only' areas would be initialized using special instructions or combinations of protect key/ program mask. Normal access to such lines would not invoke the cross interrogate mechanism, however.

It may be desirable to group such read-only items in 4K pages, so that their status could be indicated within the Directory Look-aside Table (DLAT) rather than the Cache Directory.

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