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Browse Prior Art Database

Wait-Post Lookaside Table

IP.com Disclosure Number: IPCOM000049497D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Goldstein, BC: AUTHOR [+2]

Abstract

The following reduces validity checking overhead, reduces disruption of cache and I-stream during in-line servicing, and improves response time and lock contention.

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Wait-Post Lookaside Table

The following reduces validity checking overhead, reduces disruption of cache and I-stream during in-line servicing, and improves response time and lock contention.

Currently, when a POST is issued to an ECB (Event Control Block) which contains an RB (Request Block) address, POST, while holding critical MVS (Multiple Virtual Spaces) functional locks, starts from the beginning of the TCB (Task Control Block) chain, searching for that RB in order to validate the request. This search is a linear one. Pictorially: (see original).

While there are usually many TCBs associated with a given memory, there are few in active ECB (RB) suspension. Thus, on a POST, the normal task to be resumed is usually the last one that issued WAIT.

The concept set forth associates with a memory (ASCB (Address Space Control Block)) a wrap-around "lookaside" stack of finite size (say, 4 entries initialized to zero).

When a WAIT is issued, an entry in the stack is allocated. If all are already in use, then one is stolen. In the entry, the ECB address and RB addresses are stored.

On a subsequent POST, this stack is first searched if the ECB and RB are found, then POST completes its integrity check and can mark the suspended TCB as resumed.

If the ECB and RB are not found on the stack, then the normal POST search is performed.

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