The open-source Xen hypervisor virtualization project is getting a major new feature release this week that expands deployment options for ARM and cloud environments.
Konrad Rzeszutek Wilk, Software Development Manager at Oracle, and a Xen Project advisory board member, told ServerWatch that in the new Xen 4.4 release ARM support is no longer experimental and has matured significantly with major usability and performance improvements.
"The hypercall ABI is stable and will be maintained for backward compatibility," Wilk said. "This means that going forward, kernel communication to the hypervisor will be supported in this fashion."
Wilk added that in the ARM world, hardware compatibility is often a challenge. To that end the Xen project has done the hard work to add support for AppliedMicro’s X-Gene, the Arndale Board, Calxeda ECX-2000, TI OMAP5 and the Allwinner SunXi boards.
Xen 4.4 also provides a new PVH (Paravirtualized Hardware) mode that will further improve virtualized server performance. Wilk explained that the Xen Project Hypervisor has an ParaVirtualization mode (PV) for guest virtual machines wherein there are no emulated devices present. PV mode eliminates extra overhead and minimizes the attack vector.
"The PVH takes PV mode and, instead of the hypervisor doing most of the kernel bookkeeping, the hardware extensions (EPT, NPT) take care of it," Wilk said. "The end result is that the overhead of doing this in an HVM (Hardware Virtual Machine) container is much lower, providing lower latency and higher throughput for guests."
Xen 4.4 will also be beneficial for cloud deployments thanks to an improved event channel. Xen is already widely used in the cloud, most notably by Amazon.
"The event channel changes (also known as FIFO events) revamp how events (aka interrupts, but much more lightweight) are delivered and processed," Wilk said. "The end result is that we can easily launch thousands (and more) of guests on one host. That translates to higher density with faster response time."
Support for SPICE
With Xen 4.4 support for the SPICE protocol is also being added. SPICE is noteworthy in that it is an effort led by Red Hat and is typically thought of as being a desktop virtualization technology closely tied to the KVM hypervisor.
George Dunlap, Xen 4.4 release coordinator and maintainer for the scheduler subsystem, told ServerWatch that the Xen Project software is a community-developed open source project, which means anyone who is willing to invest the time to code can influence the direction of the project.
"SPICE support was contributed by a very motivated user who wanted to use it himself," Dunlap said.
Dunlap explained that like a lot of KVM features, SPICE is actually in qemu — and qemu is actually shared between KVM and the Xen Project hypervisor.
"In fact, anyone willing to get their hands dirty typing arcane runes into their config files could use a number of KVM features in Xen currently," Dunlap said. "So all it really took was someone willing to add the plumbing to make the SPICE interfaces in qemu usable through the officially supported Xen interface without the arcane runes."
From a user perspective, Dunlap said that with the addition of SPICE, an organization employing multiple hypervisors now has the option to use SPICE as a common remote interface. The fact that Xen 4.4 adds SPICE support is a testament to the power of open source and the open development model in Dunlap's view.
"If our members, or even just one motivated individual, see a need for new technologies, there's the opportunity to share code and influence the direction of the project," Dunlap said.