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CPU-I/0 Overlap in Computer Systems and Queueing Network Models

IP.com Disclosure Number: IPCOM000128563D
Original Publication Date: 1979-Dec-31
Included in the Prior Art Database: 2005-Sep-16
Document File: 5 page(s) / 22K

Publishing Venue

Software Patent Institute

Related People

Steven C. Bruell: AUTHOR [+3]

Abstract

Many simplifying assumptions are required to derive a mathematical solution for a queueing network model. One such assumption states that individual jobs receive service from one and only one station at a time (such as with overlap between CPU and I/0 processing). In this report we investigate the effects on the performance measures predicted by a queueing network model with and without intra-job overlap. We also study the amount of CPU-I/0 overlap within jobs in an actual computer system.

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THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

CPU-I/0 Overlap in Computer Systems and Queueing Network Models

by Steven C. Bruell

0400406 Computer Science Department

136 Lind Hall Institute of Technology University of Minnesota Minneapolis, Minnesota 55455 Cover design courtesy of Ruth and Jay Leavitt Technical Report 79-6 February, CPU-I/0 Overlap in Computer Systems and Queueing Network Models by Steven C . Brue7_1

Abstract

Many simplifying assumptions are required to derive a mathematical solution for a queueing network model. One such assumption states that individual jobs receive service from one and only one station at a time (such as with overlap between CPU and I/0 processing). In this report we investigate the effects on the performance measures predicted by a queueing network model with and without intra-job overlap. We also study the amount of CPU-I/0 overlap within jobs in an actual computer system.

Introduction

one simplifying assumption underlying the solution.of queueing network models is that individual jobs receive service from only one station at a time. This assumption thus precludes a single job from receiving service from two or more stations simultaneously, such as with overlap between CPU and I/0 processing. Queueing network models do permit concurrent use of all the service centers in the network, but this is accomplished by allowing different jobs to occupy the various stations. These models distinguish between concurrent use of stations across all jobs in the network and concurrent use of stations by a single job. We refer to this latter case as intra-job overlap.

In many actual systems, much effort is expended on the design and implementation of mechanisms, such as sub-tasking and double or circular I/0 buffering, which permit individual jobs to use the CPU and I/0 devices simultaneously.

In this paper we investigate the effect on the performance measures predicted by a queueing network model with. and without intra-job overlap. Also, from an empirical study we measure the amount of CPU-I/0 overlap within jobs in an actual computer system.

Overlapped Usage of Service Centers

A job in a computer system typically requires both computational and input/output processing. The job (or program) may be viewed as an alternating sequence of CPU and I/0 processing intervals. Each such interval may be preceded by a queueing delay (while a job waits for an unavailable resource).

University of Minnesota Page 1 Dec 31, 1979

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CPU-I/0 Overlap in Computer Systems and Queueing Network Models

In a real system which permits intra-job overlap, a more realistic job description is that a CPU processing interval proceeds in parallel with I/0 processing intervals. The CPU interval may eventually be blocked pending the completion of the I/b processing interval. Thus, a job operating in a real system has the potential of achieving varying degrees of overlapped usage of resources; it can use the CPU and...