KVM, Xen battle for hacker interest: Horms

Simon Horman

If the Linux virtualisation space wasn't heated enough, the open source hypervisors Kernel Virtual Machine (KVM) and Xen are now duking it out for independent developer interest, according to Xen hacker Simon "Horms" Horman.

Horman is attending this year's linux.conf.au conference in Hobart while remaining close to his day job as a senior Linux developer at VA Linux Systems Japan K. K, but based in the Sydney office.

While Xen has attracted a lot of commercial support from big-name software vendors like Citrix, Novell and Oracle, Horms believes it is losing its appeal to - and contributions from - independent kernel developers due to sheer geek value.

"It's the nature of the maturity of a technology. The developers are drawn to the bleeding edge," Horms said. "There is a lot more interesting things happening in the KVM space now."

"The kind of features that need to go into Xen are 'enterprise-level' and not that interesting to many people so you will get those features developed by paid developers."

He said Xen is more mature so if a business is going to deploy virtualisation software now it will be either Xen or VMware; however, "if you ware looking at the future" KVM is in a "strong position" because of the way it is already integrated into the Linux kernel.

While Xen "sparked a lot of activity" on the development side, has more management tools and the hardware began to support it, Horms believes the game is changing with Red Hat's support for KVM.

"The decision is a maintainbility reason," he said. "Xen hasn't been integrated into Linux. It is coming, but slowly."

"It's a non-trivial patch for Xen and to keep that up to date is a lot of work and it's all being done by the vendors to date. They are working on the paravirt-ops code which basically abstracts out what you need to run Xen and support VMware. If it's going to get into mainline it will be available and instead of Xen kernel it will be like SMP support."

Horms said it could take another six months to a year before Xen gets into the mainline kernel.

"If that happens I would expect fewer distributions to stop using it," he said.

"The advantage of getting code in the kernel is you will get more eyes looking at it and that has helped KVM a lot. There is a long history on resistance from kernel developers to Xen. At the very least you will be able to run an up-to-date kernel as the host without a major porting effort and that is a huge win for users and distros."

In addition to the integration benefits, "the user experience should improve almost straight away".

Xen is working to strip out the need for a full-blown Linux instance, Horms said, and the idea is to shrink it to "make it easer to trust it".

"One of the main criticisms of KVM is you will always need to have a Linux instance," he said. "I suspect the Xen approach will lead to fewer lines of code."

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