Virtualization polling engine (VPE): using dedicated CPU cores to accelerate I/O virtualization

Virtual machine (VM) technologies are making rapid progress and VM performance is approaching that of native hardware in many aspects. Achieving high performance for I/O virtualization remains a challenge, however, especially for high speed networking devices such as 10 Gigabit Ethernet 10 GbE) NICs. Traditional software-based approaches to I/O virtualization usually suffer significant performance degradation compared with native hardware. Hardware-based approaches that allow direct device accessin VMs can achieve good performance, albeit at the expense of increased hardware cost and increased complexity in achieving tasks such as VM checkpointing, migration, and record/reply. Recently, the trend in microprocessor design has shifted from achieving higher CPU frequencies to putting more cores in a single chip, thus the cost of each core is rapidly decreasing. In this paper, we propose a new I/O virtualization approach called the Virtualization Polling Engine (VPE). VPE introduces a concept called virtualization onload, which takes advantage of dedicated CPU cores to help with the virtualization of I/O devices by using an event-driven execution model with dedicated polling threads. It can significantly reduce virtualization overhead and achieve performance close to the hardware-based approaches without requiring special hardware support. Using our VPE approach, we developed a prototype called KVM-VPE to provide Ethernet virtualization support for KVM. Our experiments in a 10GbE testbed showed that VPE significantly outperformed the original KVM. In Netperf TCP tests our prototype achieved over 5 times the bandwidth for transmitting (Tx) and over 3 times the bandwidth for receiving (Rx) compared with the original KVM. KVM-VPE also supports direct user application access to the virtual Ethernet interfaces and achieved 7.4 μs end-to-end latency between two VMs on different machines in our testbed. Overall, our research demonstrated that VPE is a promising approach to high performance I/O virtualization in the coming multicore era.