Paravirtual Remote I/O

Abstract

The traditional "trap and emulate" I/O paravirtualization model conveniently allows for I/O interposition, yet it inherently incurs costly guest-host context switches. The newer "sidecore" model eliminates this overhead by dedicating host (side)cores to poll the relevant guest memory regions and react accordingly without context switching. But the dedication of sidecores on each host might be wasteful when I/O activity is low, or it might not provide enough computational power when I/O activity is high. We propose to alleviate this problem at rack scale by consolidating the dedicated sidecores spread across several hosts onto one server. The hypervisor is then effectively split into two parts: the local hypervisor that hosts the VMs, and the remote hypervisor that processes their paravirtual I/O. We call this model vRIO---paraVirtual Remote I/O. We find that by increasing the latency somewhat, it provides comparable throughput with fewer sidecores and superior throughput with the same number of sidecores as compared to the state of the art. vRIO additionally constitutes a new, cost-effective way to consolidate I/O devices (on the remote hypervisor) while supporting efficient programmable I/O interposition.