Prioritizing verification via value-based correctness criticality

Microprocessors are becoming increasingly susceptible to soft errors due to the current trends of semiconductor technology scaling. Traditional redundant multi-threading architectures provide good fault tolerance by re-executing all the computations. However, such a full re-execution significantly increases the demand on the processor resources, resulting in severe performance degradation. To address this problem, this paper introduces a correctness criticality based filter checker, which prioritizes the verification candidates so as to selectively do verification. Binary Correctness Criticality (BCC) and Likelihood of Correctness Criticality (LoCC) are metrics that quantify whether an instruction is important for reliability or how likely an instruction is correctness-critical, respectively. A likelihood of correctness criticality is computed by a value vulnerability factor, which is defined by the numerically significant bit-width used to compute a result. The proposed technique is accomplished by exploiting information redundancy of compressing computationally useful data bits. Based on the likelihood of correctness criticality test, the filter checker mitigates the verification workload by bypassing instructions that are unimportant for correct execution. Extensive measurements prove that the LoCC metric yields quite a wide distribution of values, indicating that it has the potential to differentiate diverse degrees of correctness criticality. Experimental results show that the proposed scheme accelerates a traditional fully-fault-tolerant processor by 1.7 times, while it reduces the soft error rate to 18% of that of a non-fault-tolerant processor.