Thread shadowing: On the effectiveness of error detection at the hardware thread level

Dynamic thread duplication is a known redundancy technique for multi-cores. Recent research applied this concept to hybrid multi-cores for error detection and introduced thread shadowing that runs hardware threads in the reconfigurable cores and compares their outputs for deviation at configurable signature levels. Previously published work evaluated this concept in terms of performance, error detection latency and resource consumption. In this paper we report on the error detection capabilities of thread shadowing by presenting an extensive fault injection campaign. We employ the Xilinx Soft Error Mitigation Controller for fault injection and the Xilinx Essential Bit facility to limit the fault injections to relevant bits in the configuration bitstream. Our findings from fault injection experiments with a sorting benchmark are threefold: First, up to 98% of all errors are detected by the operating system of the hybrid multi-core supported by thread shadowing. Second, thread shadowing's signature levels provide a useful trade-off between detected errors and effort needed, with around 5% of all errors detected in calls to operating system functions and around 52% of errors detected in memory accesses of the hardware thread. Third, essential bit testing is effective and cuts down the amount of bits to be tested by a factor of 14.48 compared to the total amount of bits available in the configuration address space.