STOCK: Stochastic Checkers for Low-overhead Approximate Error Detection

Neel Gala, Swagath Venkataramani, A. Raghunathan, V. Kamakoti
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Abstract

Designing reliable systems, while eschewing the high overheads of conventional fault tolerance techniques, is a critical challenge in the deeply scaled CMOS and post-CMOS era. To address this challenge, we leverage the intrinsic resilience of application domains such as multimedia, recognition, mining, search, and analytics where acceptable outputs are produced despite occasional approximate computations. We propose stochastic checkers, wherein a stochastic logic based realization of the circuit is used as an error checker, and the original circuit's output is declared to be correct if it lies within a certain range of the checker's output. The key benefit of stochastic checkers is that the intrinsic compactness of stochastic logic leads to greatly reduced overheads. However, due to the approximate nature of stochastic circuits, errors that cause the output to be within a certain range of the correct value may not be detected (missed coverage). In addition, some correct outputs may be incorrectly flagged as erroneous (false positives). To limit the number of missed errors and false positives, we propose a technique that uses input permuted partial replicas of the stochastic logic to improve accuracy without greatly increasing the overheads. We also address the challenge of error detection latency (due to the bit-serial nature of stochastic logic) through progressive checking policies that produce an early decision based on a prefix of the checker's output bitstream. We evaluate stochastic checkers on hardware implementations of a suite of error-resilient applications, and demonstrate that they can lead to greatly reduced overheads (29.5% area and 21.5% power, on average) compared to traditional fault tolerance techniques, while achieving very high coverage (average of 99.5%) and very low false positives (average of 0.1%).
库存:用于低开销近似错误检测的随机检查器
设计可靠的系统,同时避免传统容错技术的高开销,是深度扩展CMOS和后CMOS时代的关键挑战。为了应对这一挑战,我们利用了应用程序领域的内在弹性,例如多媒体、识别、挖掘、搜索和分析,尽管偶尔会进行近似计算,但可以产生可接受的输出。我们提出了随机检查器,其中使用基于随机逻辑的电路实现作为错误检查器,如果原始电路的输出位于检查器输出的一定范围内,则声明其正确。随机检查器的主要优点是随机逻辑固有的紧凑性大大降低了开销。然而,由于随机电路的近似性质,导致输出在正确值的一定范围内的错误可能无法被检测到(遗漏覆盖)。此外,一些正确的输出可能被错误地标记为错误(误报)。为了限制遗漏错误和假阳性的数量,我们提出了一种技术,该技术使用随机逻辑的输入排列部分副本来提高准确性,而不会大大增加开销。我们还通过渐进式检查策略解决了错误检测延迟的挑战(由于随机逻辑的位串行性质),该策略基于检查器输出比特流的前缀产生早期决策。我们评估了一套容错应用程序的硬件实现上的随机检查器,并证明与传统的容错技术相比,它们可以大大降低开销(平均29.5%的面积和21.5%的功耗),同时实现非常高的覆盖率(平均99.5%)和非常低的误报(平均0.1%)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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