Yunfang Tai’s research while affiliated with Chinese Academy of Sciences and other places

Virtualization is one of the hot topics in operating systems. However, virtualization on MIPS servers remains stagnant after the first attempt was done in late 1990s. The previous solutions seem not to meet the needs of modern servers and many aspects of them can still be improved. This paper introduces KVM-Loongson, an efficient virtualization solution for MIPS based on KVM. Paravirtualization is adopted to improve the performance of CPU virtualization and the clock accuracy. It can also reduce the memory virtualization overheads which are caused by three factors existing in virtualization on MIPS. Our experience also reveals that hardware virtualization support for MIPS is still needed on the aspect of efficiency. The whole work is done on boards with Loongson-3A CPUs which are quad core processors based on MIPS64 ISA. Performance evaluations show that programs of SPEC CINT2000 on the virtual machine can achieve averaging 94% their performance on the native machine when running single virtual machine.

Memory virtualization plays an important role in system virtualization. However, traditional memory virtualization solutions are usually for those architectures with hardware-managed TLBs, such as x86, ARM and so on. The solutions for architectures with software-managed TLBs are rarely mentioned. This paper presents three different memory virtualization solutions for architectures with software-managed TLBs. The difference is that different methods are used to tackle guest TLBs. One is emulating the guest TLBs by software, another is eliminating the guest TLBs and the third is emulating guest TLBs by hardware. After comparisons on hardware platform with MIPS CPUs, it can be seen that the method eliminating guest TLBs can increase the memory bandwidth by more than 100% on average compared to the method emulating guest TLBs by software. After comparisons on simulation platform with MIPS CPUs, it can be seen that the method emulating guest TLBs by hardware would cause about 135% more extra exceptions than the method eliminating guest TLBs. The method eliminating guest TLBs is a good choice when full virtualization is not necessary on the CPUs with software-managed TLBs.