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Increased power densities (and resultant temperatures) and other effects of device scaling are predicted to cause significant lifetime reliability problems in the near future. In this paper, we study two techniques that leverage microarchitectural structural redundancy for lifetime reliability enhancement. First, in structural duplication (SD), redundant microarchitectural structures are added to the processor and designated as spares. Spare structures can be turned on when the original structure fails, increasing the processorýs lifetime. Second, graceful performance degradation (GPD) is a technique which exploits existing microarchitectural redundancy for reliability. Redundant structures that fail are shut down while still maintaining functionality, thereby increasing the processorýs lifetime, but at a lower performance. Our analysis shows that exploiting structural redundancy can provide significant reliability benefits, and we present guidelines for efficient usage of these techniques by identifying situations where each is more beneficial. We show that GPD is the superior technique when only limited performance or cost resources can be sacrificed for reliability. Specifically, on average for our systems and applications,GPD increased processor reliability to 1.42 times the base value for less than a 5% loss in performance. On the other hand, for systems where reliability is more important than performance or cost, SD is more beneficial. SD increases reliability to 3.17 times the base value for 2.25 times the base cost, for our applications. Finally, a combination of the two techniques (SD+GPD) provides the highest reliability benefit.
Srinivasan et al. (Sun,) studied this question.