Relaxed Determinism: Making Redundant Execution on Multiprocessors Practical

Given that the majority of future processors will contain an abundance of execution cores, redundant execution can offer a promising method for increasing the availability and resilience against intrusions of computing systems. However, redundant execution systems rely on the premise that when external input is duplicated identically to a set of replicas executing the same program, the replicas will produce identical outputs unless they are compromised or experience an error. Unfortunately, threaded applications exhibit non-determinism that breaks this premise and current redundant execution systems are unable to account for this non-determinism, especially on multiprocessors. In this paper, we introduce a method called relaxed determinism that is utilized by our system, called Replicant, to support redundant execution with reasonable performance while tolerating non-determinism.