Ditto Processor

Concentration of design effort for current single-chip Commercial-Off-The-Shelf (COTS) microprocessors has been directed towards performance. Reliability has not been the primary focus. As supply voltage scales to accommodate technology scaling and to lower power consumption, transient errors are more likely to be introduced. The basic idea behind any error tolerance scheme involves some type of redundancy. Redundancy techniques can be categorized in three general categories: (1) hardware redundancy, (2) information redundancy, and (3) time redundancy. Existing time redundant techniques for improving reliability of a superscalar processor utilize the otherwise unused hardware resources as much as possible to hide the overhead of program re-execution and verification. However, our study reveals that re-executing of long latency operations contributes to performance loss. We suggest a method to handle short and long latency instructions in slightly different ways to reduce the performance degradation. Our goal is to minimize the hardware overhead and performance degradation while maximizing the fault detection coverage. Experimental studies through microarchitecture simulation are used to compare performance lost due to the proposed scheme with non-fault tolerant design and different existing time redundant fault tolerant schemes. Fourteen integer and floating-point benchmarks are simulated with 1.8~13.3% performance loss when compared with non-fault-tolerant superscalar processor.