2011/4/4 Clint Byrum <cl...@ubuntu.com>: > Maybe we should ask though. Adding Xen back in means less resources > for KVM, so the KVM users' opinions matter quite a bit.
The very short version: I'm fine with Ubuntu getting Xen support again, but I don't think it needs to be in main. We chose KVM as our preferred, supported hypervisor a long time ago. We've been telling people for years that it's what they should be using, and lots of great effort has been put into the integration work. The arguments against KVM were mostly about the hardware requirements, but if we could live with that in 2007, I'd be surprised if we couldn't today, since the percentage of server hardware that doesn't work with KVM has severely declined. Any decision will have supporters and opponents, and I firmly believe that making a decision is the right thing to do. I believe there's a lot of value (for everyone involved) in having firm answers to even tough questions. Ubuntu, for instance, is a free operating system. No-one has to ask over and over whether it's still free, because we've been very clear from the beginning that that's how we roll. Similarly, you won't find any closed-source applications on an Ubuntu CD. If you're wanting to distribute closed source applications, don't bother asking if you can put it on one of the Ubuntu CD's. No matter how popular your software is, or how many people vote for it on a mailing list or on Ubuntu Brainstorm, it's not going to happen. We're also not going to switch to the FreeBSD kernel on a whim. Every decision we make defines us, whether it's an additive or subtractive one. Every decision we fail to make, weakens us. When we chose KVM as our preferred hypervisor, it wasn't a decision to use it in Hardy and revisit that decision every release following it (that would have made it almost a non-decision). It wasn't a decision to run this or that benchmark every 6 months, and whichever was in the lead would be the preferred, supported hypervisor that we'd go out and praise, and the rest would be deprecated until 6 months later when the numbers would be slightly different. We made the decision even though KVM was still quite young, and none of the other major distros were shipping it. We made the decision to ship it, support it, stand behind it, and help it grow. Ubuntu's hypervisor was KVM. I happily stand by that decision. I believe KVM's design is superior. KVM immediately benefits from improvements made to the Linux kernel. If power management improves in the Linux kernel, your KVM host's power management improves. If the scheduler improves, KVM benefits. If memory management improves, KVM benefits. KVM is part of the Linux kernel, while Xen has its own kernel. I'm not talking about the dom0, I'm talking about the Xen hypervisor on top of which the dom0 and domU's run. This difference means that many improvements in Linux need to be accommodated for or mimicked in Xen before you get the benefits there[1]. To use KVM, you load a module that turns your regular Linux kernel into a hypervisor. To run Xen, you boot a completely different kernel on top of which you run a dom0. For the most part, you don't see the difference, because distributors have put a lot of work into making this change seamless, but effectively, you're not running Linux anymore as your kernel. Anthony Liguori (one of the KVM and QEmu developers) said it quite well[2]: "The whole situation is somewhat absurd though. It's like if the distributions shipped a NetBSD kernel automatically and switched to using it when you wanted to run a LAMP stack." Linux is a fine hypervisor on its own. It may not be perfect, but I'd prefer we focus on identifying and fixing those issues If someone thinks Xen is sufficiently cool, I'd encourage them to put some effort getting it into shape in Ubuntu. I don't think we should divert any of the existing attention on kvm/libvirt/friends to Xen. I don't think we can afford it. [1]: This page on power management with Xen is a good example: http://wiki.xensource.com/xenwiki/xenpm [2]: http://blog.codemonkey.ws/2008/05/truth-about-kvm-and-xen.html -- Soren Hansen | http://linux2go.dk/ Ubuntu Developer | http://www.ubuntu.com/ OpenStack Developer | http://www.openstack.org/ -- ubuntu-server mailing list ubuntu-server@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-server More info: https://wiki.ubuntu.com/ServerTeam