An enhanced end-to-end transparent clock mechanism for the kernel-based virtual machines
Mingwu Yao, Huang Zhenlin · 2017
Keeping a high-precision time base in cloud clusters is still a big challenge, even using the Precision Time Protocol version 2 (PTPv2) specified in IEEE 1588. One of the main factors on this issue is that too many uncertainties in the network path from the master clock to the slave one, which is likely residing on the Kernel-based Virtual Machine (KVM). The Transparent Clock (TC) of PTPv2 may be useful to solve this issue. However, at present the network I/O path in the virtual machine environment has not been considered in such works, which seriously affect the performance of the synchronization accuracy. In this work, we make improvements in the kernel network stack to manipulate the PTP frames to record the residence time for the path from the physical machine to the virtual machine, making its network I/O architecture an End-to-End Transparent Clock (E2E TC). Although the idea of E2E TC for more accurate synchronization is not new, there is no such implementation publicized for the virtualized environment, as far as we know. The proposed mechanism is specifically tailored to make latency corrections for the neglected routing path between the physical Network Interface Card (NIC) and the virtual machines. Extensive experiments and tests show that this approach makes quite significant improvement of about 50%.