Paratick: Reducing Timer Overhead in Virtual Machines

To this day, efficient timer management is a major challenge in virtualized environments. Contemporary timekeeping techniques in guest kernels frequently interact with timer hardware, which requires continual and costly hypervisor interference. This paper proposes the concept of virtual scheduler ticks, which significantly reduces the need for guests to interact with timer hardware through the use of paravirtualization. Guests no longer program scheduler ticks, but rely on the host to inject its own ticks into vCPUs upon VM entry. We implemented virtual scheduler ticks in Linux/KVM under the name paratick. We present a thorough performance analysis of paratick in the context of hardware-assisted X86 virtualization. Paratick reduces VM exits by up to 80%, enhancing system throughput by up to 125% and execution time by up to 15% for multithreaded applications relying heavily on blocking synchronization. For I/O-intensive applications, these numbers are respectively 45%, 30% and 25%.