Enhancing the I/O system for virtual machines using high performance SSDs

Abstract

Storage I/O in VM (Virtual Machine) environments, which requires low latency, becomes problematic as the fast storage such as SSDs (Solid-State Drives) is currently in use. The low performance problem in the VM environment is caused by 1) the presence of additional software layer such as guest OS, 2) context switching between VM and host OS, and 3) scheduling delay for I/O process. These factors do not cause serious problems in the case of using HDD which leads to high latency batching. However, there will be significant performance degradation when fast storage devices are used. To address this problem, we have proposed the following methods to improve the performance of I/O stack in the VM environments by attempting to optimize the I/O stack: one is pipelined polling, and the other is multiple issues and multiple completions. We have found via experiments that our approach leads to increases in the performance of SSDs in a VM environment by up to 50% when multiple VM storage devices are used, and that it leads to improvements in the performance by more than 80% when a single VM storage device is used, with the CPU utilization reduced by up to 25%.