Ask the world's most famous kernel developer what he thinks of the virtualization wars going on the Linux community between KVM and Xen and you'll hear a condemnation (of a sort) of them both. "I'm not a virtualization kind of guy. I think virtualization is evil," Linus Torvalds told the crowd at LinuxCon on Wednesday during his keynote interview session with Greg Kroah-Hartman.
Virtualization takes Torvalds away from the hardware and that's not where he wants to go. "I built a kernel because I wanted to get my hands grubby with things like I/O ports."
Nevertheless, he did offer somewhat of a new vote of confidence toward Xen, a project that was formerly the subject of much famous flaming on the kernel developer mail list. "I told them, 'Look at what you sent me and look at what KVM sent me and ask yourself why do I like the KVM people more than I like you,'" he explained. Xen caused its own messy bed by not working well with the Linux kernel team, kernel experts say. The distro makers were ticked that the Xen team didn't always keep up with the latest changes to the kernel, so supporting it in their downstream editions would mean they would have to take on the burden of updating it.
But, not content to hand Linux users neatly into the hands of Red Hat's KVM, which had long ago been accepted into the kernel, the Xen folks changed their ways. "Xen developers listened to the feedback and they are now in the mainline kernel," say Torvalds. "They started thinking about how they look to [the people not on their team]. They got it. I used to dread pull requests from the Xen people. Now I don't."
Acceptance of the source Xen code for Xen's Dom0 into the kernel was a milestone for the Xen.org community achieved in June.
So then, given the history, which one does Torvald's prefer? Well, obviously, neither, as he's a guy that likes making software work directly with hardware. When an attendee asked, he merely said, "Xen is a different mind set and has different HW constraints than KVM. We support choice so we do both."
However kernel driver guru Kroah-Hartman was less circumspect and spoke out in favor of KVM. "I do like KVM" he said, saying he thought its approach was cleaner and more elegant, praise the world has heard before for the hypervisor under Red Hat's dominion by the Linux kernel team. He also added, "This is not my corporate answer. My company has invested hugely in Xen." Kroah-Hartman works for SUSE, formerly of Novell but recently acquired by Attachmate.
Jim Zemlin, executive director of The Linux Foundation, perhaps summed it up best. In his closing remarks he said, "For all you bloggers out there, I have your headline for you: `Linux Torvalds says that virtualizaiton is evil, world disagrees.'"