Breaking the I/O Virtualization Bottleneck

Virtualization has helped improve hardware utilization tremendously, but its full potential has not yet been realized. Virtualization technologies all share and virtualize a single physical port of the network adapter through software for the I/O needs of the virtual machines. All of that software battles to make I/O decisions for the virtual machines, which causes traffic jams, which slow the I/O performance and limit the number of virtual machines a physical server can run.

To address this issue, PCI-SIG, the special interest group that owns and manages PCI specifications as open industry standards, introduced a suite of specifications for Single Root I/O Virtualization (SR-IOV) specifications to allow multiple operating systems to share a physical interconnect.

Now Dell, Intel and Citrix are putting the PCI-SIG specs into action and will be demonstrating SR-IOV technology at the Intel Developers Forum 2009. IDF attendees can check out the showcase at exhibit booth #711 and hear all the technical brilliance straight from Dell, Intel and Citrix experts.

Here is the gist of how it works. SR-IOV allows hardware implementation of virtual network interface cards (NICs) or virtual functions without software emulation. In this way, a single I/O hardware is subdivided logically to appear as up to 256 virtual NICs and each virtual function is assigned independently and directly to a virtual machine, bypassing the software bottlenecks in the hypervisor to achieve near native performance. It also provides precise per-VM control for the connection speed and QoS. This specific demo uses Intel VT-d and Intel® 82599 10 Gigabit Ethernet device and allows multiple virtual machines (VMs) running on Citrix XenServer on Dell PowerEdge R710 with Intel® Xeon® processor 5500 to directly share I/O devices.

SR-IOV holds great promise. It improves data throughput and increase performance, efficiency, and scalability with high performance I/O devices, while preserving flexibility and mobility with live migration support. In preliminary lab tests with Dell, Intel and Citrix, this technology reduces processor utilization, Increases bandwidth to virtual machines and improves data transfer rates across the network.

Another benefit is that SR-IOV can save reduce capital expenditure as it doesn’t require special network infrastructure. It works with existing standard 10GE Ethernet switches on existing network infrastructures. Some other virtualization solutions rely on proprietary technologies requiring rip-and-replace upgrades to networks to get the benefits of I/O virtualization. SR-IOV technology further cuts hardware costs by reducing the number of physical network cards, and switch ports, as well as cabling for even more consolidation in a virtualized environment.

Rich Hernandez, PG Development Engineer Strategist in Dell Server Advanced Engineering Group has been working on this technology. Here he is with a brief overview:

About the Author: Matt McGinnis