Capo: A software-hardware interface for practical deterministic multiprocessor replay

While deterministic replay of parallel programs is a power-ful technique, current proposals have shortcomings. Specifi-cally, software-based replay systems have high overheads on multiprocessors, while hardware-based proposals focus only on basic hardware-level mechanisms, ignoring the overall re-play system. To be practical, hardware-based replay systems need to support an environment with multiple parallel jobs running concurrently — some being recorded, others being replayed and even others running without recording or re-play. They also need to manage limited-size log buffers. This paper addresses these shortcomings by introduc-ing, for the first time, a set of abstractions and a software-hardware interface for practical hardware-assisted replay of multiprocessor systems. The approach, called Capo, intro-duces the novel abstraction of the Replay Sphere to sepa-rate the responsibilities of the hardware and software com-ponents of the replay system. In this paper, we also design and build CapoOne, a prototype of a deterministic multi-processor replay system that implements Capo using Linux and simulated DeLorean hardware. Our evaluation of 4-processor executions shows that CapoOne largely records with the efficiency of hardware-based schemes and the flex-ibility of software-based schemes