I/O pass-through lets us have our virtual cake and eat it, too

posted by John Troyer (VMWare) on August 22, 2008

On stage at IDF, Intel EVP Pat Gelsinger showed off the future Nehalem platform and with it, supporting technology from VMware called VMDirectPath. Here’s an overview of the keynote from InformationWeek. If you look at the video webcast of Pat Gelsinger’s keynote, at about the 34:50 mark Pat talks with VMware’s Rich Brunner about VMDirectPath. (N.B., I had no problem viewing this webcast on Windows with IE, but had difficulty with Mac/Firefox.)

Essentially, current virtual network adapters have a CPU overhead for high-speed I/O devices, such as 10 Gigabit Ethernet. In 2009, VMware expects to be able to bypass emulation for the virtual network adapter and interact directly with the hardware. This uses Intel VT-d to do address translation and protection. In the keynote, they demonstrate a 1.7x performance increase in the virtual machine using VMDirectPath, because now the CPU is not doing network device emulation.

On the technology showcase floor, VMware’s John Kennedy gives more context on Intel VT-d and VMware VMDirectPath.

As John says, once you connect the virtual machine to a physical device, things get complicated if you want to use the advantages of virtualization, like live migration (VMotion) of the virtual machine to another physical server, or sharing the device among several virtual machines. The longer-term vision of I/O and “Virtualization 3.0” was discussed at session IOSS003, I/O Pass-Through Methologies for Mainstream Virtualization Usage from Intel’s Sean Varley and VMware’s Howie Xu. (pdf presentation) The technologies supporting VMDirectPath extend beyond VT-d to the rest of the VT alphabet, including VT-x, VT-c, and VMDq, as well as to standards like Single-Root I/O Virtualization (SR-IOV). VMDirectPath will have a plug-in architecture that lets the hardware makers differentiate their offerings while still allowing the virtual machine to have no dependencies on the hardware it’s running on.

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tagged: idf, idf2008, networking, pass-through, virtualization, vmdirectpath, vmware