Proteus: a flexible and fast software supported hardware logging approach for NVM.

Emerging non-volatile memory (NVM) technologies, such as phase-change memory, spin-transfer torque magnetic memory, memristor, and 3D Xpoint, are encouraging the development of new architectures that support the challenges of persistent programming. An important remaining challenge is dealing with the high logging overheads introduced by durable transactions. In this paper, we propose a new logging approach, Proteus for durable transactions that achieves the favorable characteristics of both prior software and hardware approaches. Like software, it has no hardware constraint limiting the number of transactions or logs available to it, and like hardware, it has very low overhead. Our approach introduces two new instructions: log-load creates a log entry by loading the original data, and log-flush writes the log entry into the log. We add hardware support, primarily within the core, to manage the execution of these instructions and critical ordering requirements between logging operations and updates to data. We also propose a novel optimization at the memory controller that is enabled by a persistent write pending queue in the memory controller. We drop log updates that have not yet written back to NVMM by the time a transaction is considered durable. We implemented our design on a cycle accurate simulator, MarssX86, and compared it against state-of-the-art hardware logging, ATOM [19], and a software only approach. Our experiments show that Proteus improves performance by 1.44--1.47× depending on configuration, on average, compared to a system without hardware logging and 9--11% faster than ATOM. A significant advantage of our approach is dropping writes to the log when they are not needed. On average, ATOM makes 3.4× more writes to memory than our design.