COSPlay: Leveraging task-level parallelism for high-throughput synchronous persistence

Abstract

A key challenge in programming crash-consistent applications for Persistent Memory (PM) is achieving high performance while controlling the order of PM updates. Managing persist ordering from the CPU typically requires frequent synchronization points, which expose the PM's high persist latency on the execution's critical path. To mitigate this overhead, prior proposals relax the persistency model and decouple persistence from the program's volatile execution, delegating persistence ordering to specialized hardware mechanisms such that persistent state lags behind volatile state. In this work, we identify the opportunity to mitigate the effect of persist latency by leveraging the task-level parallelism available in many PM applications, while preserving the stricter semantics of synchronous persistence and the familiar x86 persistency model. We introduce COSPlay, a software-hardware co-design that employs coroutines and rapid userspace context switching to hide persist latency by overlapping persist operations across concurrent tasks. Modest CPU extensions enable the hardware to fully overlap persists of different contexts, while preserving intra-context ordering to meet crash consistency requirements. COSPlay boosts the throughput of crash-consistent applications by up to 1.7× on systems with basic PM support. For systems with higher persist latency due to added backend memory operations, such as encryption and deduplication, COSPlay's performance gains grow to 2.2 - 7.3×.