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Serial Resource Control Methods

IP.com Disclosure Number: IPCOM000088287D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 102K

Publishing Venue

IBM

Related People

Melkun, BF: AUTHOR

Abstract

Described herein are three methods for improving the performance of serial resource control relative to the general Enqueue/Dequeue (ENQ/DEQ) mechanism. These methods achieve their performance by only requiring ENQ/DEQ in situations of high contention for a resource, using simple high-performance techniques, in particular Compare-And-Swap (CS) instruction logic and WAIT/POST logic, for the no-contention and low-contention cases. The examples in Figs. 1, 2 and 3 describe the methods, which progressively increase in complexity and in the ability to defer ENQ/DEQ to high contention levels. The names used are arbitrary; in actual situations they would be chosen as appropriate for the resource and its users.

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Serial Resource Control Methods

Described herein are three methods for improving the performance of serial resource control relative to the general Enqueue/Dequeue (ENQ/DEQ) mechanism. These methods achieve their performance by only requiring ENQ/DEQ in situations of high contention for a resource, using simple high- performance techniques, in particular Compare-And-Swap (CS) instruction logic and WAIT/POST logic, for the no-contention and low-contention cases. The examples in Figs. 1, 2 and 3 describe the methods, which progressively increase in complexity and in the ability to defer ENQ/DEQ to high contention levels. The names used are arbitrary; in actual situations they would be chosen as appropriate for the resource and its users.

Fig. 1: Deferring ENQ/DEQ From First Level.

This control program method uses a variable, LEVEL, common to all resource requests, to indicate resource activity. A value of Phi, the initial value, indicates no active request. A value n > Phi indicates an active request plus n-1 pending requests. Pending requests must WAIT for a common event control block (ECB), initialized to Phi, the use of which requires an ENQ on a name representing the ECB resource. The active request will POST the ECB if there are pending requests at work completion.

Fig. 2: Deferring ENQ/DEQ From First and Second Levels

This control program method also uses LEVEL, plus two ECBs, here named E1 and E2. E1 is used by a second-level pending request, and E2 by highe...