The Use of Feedback in Multiprocessors and Its Application to Tree Saturation Control

Using feedback control schemes in multiprocessor systems is proposed. In a multiprocessor, individual processors do not have complete control over, nor information about, the overall state of the system. The potential exists, then, for the processors to unknowingly interact in such a way as to degrade the performance of the system. An example of this is the problem of tree saturation caused by hot-spot accesses in multiprocessors using multistage interconnection networks. Tree saturation degrades the performance of all processors in the system, including those not participating in the hot spot activity. Feedback schemes can be used to control tree saturation, reducing degradation to memory request that are not to the hot spot, thereby increasing overall system performance. As a companion to feedback schemes, damping schemes are also considered. Simulation studies show that feedback schemes can improve overall system performance significantly and with relatively little hardware cost in many cases. Damping schemes in conjunction with feedback are shown to further improve. >

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