Under and over sharing equations relating throughput capacity, resource-sharing level and the source of thrashing in multi-thread systems

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2002-03-12
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Abstract
We propose a new, non-empirical, sharing-level version of the sharing equation, which relates throughput capacity to the level of resource sharing in a system. This sharing-level version uses a sharing-level independent variable, as opposed to a sharing-algorithm time variable in an earlier version of the equation. This sharing-level version is more fundamental, given that the resource-sharing level in a system is a more fundamental performance parameter that is more easily measured. There has to be two distinct equations, however. One is for the case of under sharing, the under-sharing equation, where the sharing level is such that the throughput is less than the peak possible with an optimum sharing level. With the under-sharing equation, throughput capacity climbs with increasing sharing level. The other equation is for the case of over sharing, the over-sharing equation, where the sharing level exceeds the optimum sharing level. With the over-sharing equation, throughput capacity decreases with increasing sharing level. The over-sharing equation also reveals the true source of thrashing, when the system is operating under extreme over sharing conditions. A single empirical sharing equation is also presented, which works reasonably well for both over and under sharing, at the cost of a somewhat less than true peak throughput capacity.
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Computer Science
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