Performance Analysis of DRAM Cache by Comparing Intel Optane DC Persistent Memory Operating Modes

Yaebin Moon, Deok-Jae Oh, Jung Ho Ahn

http://doi.org/10.5626/JOK.2020.47.10.893

Non-Volatile Memory (NVM) technology is a promising alternative to DRAM technology especially when it comes to the challenge of scaling. Recently, Intel released Optane DC Persistent Memory (DCPMM), a NVM product. The latest Intel server supports two operating modes to exploit this DCPMM: 1) Memory mode uses DCPMM as main memory and DRAM as its cache, and 2) App Direct mode uses DCPMM and DRAM as independent main memory regions, necessitating software modification for efficient utilization. In this paper, we compare the performance of these two operating modes. In the Memory mode, if the working set size of an application is smaller than the DRAM cache size or data locality is guaranteed on the application, the performance reduction caused by accessing the relatively slow DCPMM can be mostly amortized. However, as the working set size becomes larger than the DRAM size, the performance decreases as more accesses are served by DCPMM experiencing additional DRAM cache miss penalties (~70 ns). Therefore, the DRAM cache has a performance limitation due to the DRAM cache miss penalty, and using the App Direct mode may well be better in terms of performance in an environment where the working set is large and there is limited data locality.