Rainbow: Efficient memory dependence recording with high replay parallelism for relaxed memory model

Abstract

Architectures for record-and-replay (R&R) of multithreaded applications ease program debugging, intrusion analysis and fault-tolerance. Among the large body of previous works, Strata enables efficient memory dependence recording with little hardware overhead and can be applied smoothly to snoopy protocols. However, Strata records imprecise happens-before relations and assumes Sequential Consistency (SC) machines that execute memory operations in order. This paper proposes Rainbow, which is based on Strata but records near-precise happens-before relations, reducing the number of logs and increasing the replay parallelism. More importantly, it is the first R&R scheme that supports any relaxed memory consistency model. These improvements are achieved by two key techniques: (1) To compact logs, we propose expandable spectrum (the region between two logs). It allows younger non-conflict memory operations to be moved into older spectrum, increasing the chance of reusing existing logs. (2) To identify the overlapped and incompatible spectra due to reordered memory operations, we propose an SC violation detection mechanism based on the existing logs and the extra information can be recorded to reproduce the violations when they occur. Our simulation results with 10 SPLASH-2 benchmarks show that Rainbow reduces the log size by 26.6% and improves replay speed by 26.8% compared to Strata. The SC violations are few but do exist in the applications evaluated.