Exit-Less Hypercall: Asynchronous System Calls in Virtualized Processes

Abstract

Many projects of virtualized processes are emerging for less overhead than traditional virtual machines and more isolation than containers. A virtualized process uses hardware virtualization to provide a process abstraction. The virtualized processes are deemed as inefficient compared against native processes using system calls since hypercalls they use cause high-overhead context switches. However, current performance of system calls is severely damaged by Kernel Page Table Isolation (KPTI) while hypercalls are unaffected. Unexpectedly, that gives hopes for virtualized processes to reach competitive performance against native processes. In this paper, we propose and implement Exit-Less Hypercall, a new style of execution framework in virtualized processes by introducing asynchronity, new thread models and adaptive migration. We evaluate the prototype and make a detailed analysis on the impacts of context switches from the native and virtualized processes with KPTI. Moreover, the experiments also show that Exit-Less Hypercall achieves a good performance improvement of up to 121% on virtualized processes using legacy hypercalls and even outperforms native processes using legacy system calls with KPTI by 81%.