Paravirtualisation means that Xen doesn't face some VMware limits for multiprocessor servers. "I've seen excellent results on eight-way systems -- that's the biggest we have access to -- but I know people are using Xen on some 32-way systems," Pratt said.
Other Xen 3 features
Multiprocessor support isn't the only change coming. Also on tap is support for Intel's Virtualisation Technology (VT), which is expected to ease Xen's operating system compatibility, and support for the 64-bit extensions that expand memory capacity for newer x86 processors such as Intel's Xeon and Advanced Micro Devices' Opteron.
Further improvements are planned for later updates to version 3, Pratt said. One is a 'shared buffer cache', which would let separate partitions share a processor's high-speed cache memory for faster data access. Another is faster networking links among different virtual machines using an approach that will work even if a virtual machine is moved from one physical computer to another.
AMD's answer to Intel's VT is a technology code-named Pacifica. Xen support for Pacifica is a "work in progress," Pratt said.
It's likely a single version of Xen will be able to support both VT and Pacifica, Pratt said.
Details on how that is likely to happen emerged in June, when AMD programmer Elsie Wahlig proposed on Xen's mailing list a common interface to the two technologies. Wahlig worked with Pratt, another lead Xen programmer named Keir Fraser, and IBM to develop the proposal.
Intel's Jun Nakajima said Intel would help modify Xen to accommodate the change. "We are evaluating this proposal and will work on enhancing the VT-x code to provide the right level of abstraction to support other VT-x like technologies," Nakajima said. VT-x refers to the version of VT that runs on Intel's Xeon processors, as opposed to VT-i for its Itanium chips.
Xen still has a ways to go, however, Haff said. "Xen remains relatively immature compared to VMware in particular," he said. "We'll be able to say it's truly mature when it gets rolled into enterprise Linux distributions and has all the ancillary command and control tools."
Another requirement for virtual machine software will be to get certification from software companies, said Gabriel Consulting Group analyst Daniel Olds. "That's a killer in the corporate environment and will keep VMware and Xen on the outside looking in" until it's addressed, he said.
The BitKeeper snafu
Xen developers are going through some of the same growing pains as the Linux operating system with which Xen is closely allied. In April, Linux programmers abruptly shifted to a new mechanism to control the project's underlying source code, and now Xen is facing the same plight.
Linux and Xen programmers had managed their source code with a proprietary tool called BitKeeper from a company called BitMover. BitMover had permitted open-source programmers to use the tool, but the company canceled the offer this year.
"The BitKeeper issue has come at a very bad time for us, as we really don't want to change (source code managers) until 3.0 ships," Pratt said.
And there aren't any simple fixes, he added. "We're strongly considering buying some BitKeeper licenses for the key developers to tide us over. We tried a bunch of different tools, and none of them come close to BitKeeper," Pratt said.
BitMover released a tool last week to ease the transition, though. The tool lets a BitKeeper source code repository be converted to a widely used alternative, Concurrent Version System, or CVS.
