Virtual device passthrough for high speed VM networking

Abstract

Supporting network I/O at high packet rates in virtual machines is fundamental for the deployment of Cloud data centers and Network Function Virtualization. Historically, SR-IOV and hardware passthrough were thought as the only viable solution to reduce the high cost of virtualization. In previous work [15] we showed how even plain device emulation can achieve VM-to-VM speeds of millions of packets per second (Mpps), though still at least 3 times slower than bare metal. In this paper, to fill this gap, we present ptnetmap, a virtual passthrough network device (based on the netmap framework). ptnetmap allows VMs to connect to any netmap port (physical devices, software switches, netmap pipes), conserving the speed and isolation of the native netmap system, and removing the constraints of hardware passthrough. Our work includes two key features not present in previous proposals: we provide a high speed path also to untrusted VMs, and do not require dedicated polling cores/threads, which is fundamental to achieve an efficient use of resources. Besides these features, our speed is also beyond previously published values. Running on top of ptnetmap, VMs can saturate a 10 Gbit link at 14.88 Mpps, talk at over 20 Mpps to untrusted VMs, and over 70 Mpps to trusted VMs. ptnetmap extends the netmap framework, and currently supports Linux and FreeBSD guests, and QEMU/KVM host. Support for bhyve/FreeBSD host is under development.