3.6 Response

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3.6 Response

Response is an important concept in computer systems performance studies. Response time represents a measure of the period of time a user or application must wait from the point of issuing some action or command until the completion and return of control for the requested command. The typical measure used may pit the response time (an interval) against the systems load (stream of jobs). The curve may appear similar to that shown in Figure 3.4.

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Figure 3.4: Response time versus system load.

The interpretation of this curve becomes an important means to evaluate our system. In Figure 3.4 we see that the response time of our measured action sequence stays within tolerable ranges (between 1.0 and 3.0) for loads below approximately 60 percent of the capacity of the measured system. As the load increases above this point, the response climbs exponentially-reaching a saturation level when the system is fully loaded, yielding an asymptotic response time approaching infinity. One can see from this simple example the importance of response time as a measurement in modeling and evaluating systems.

The problem is in trying to determine the response of what. It may not be sufficient to look at our systems performance from only one measure or action sequence. We may be interested in a family of such action sequences, requiring a series of separate tests to study the effect of each of these measurable sequences against system load. In addition to this form of measure, we may also be interested in how these various action sequences impact each other as load increases. This would result in a family of response curves, which need to be interpreted against each other and the loads.



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Computer Systems Performance Evaluation and Prediction
Computer Systems Performance Evaluation and Prediction
ISBN: 1555582605
EAN: 2147483647
Year: 2002
Pages: 136

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