kqemu and Ubuntu

Several people have asked over the last few months about kqemu in Ubuntu. Here's a concise set of FAQs on the topic.

What is kqemu?

kqemu is a kernel module that "accelerates" QEMU virtualization by allowing guests to run some operations directly on the host's CPU. In this respect, it's similar to kvm.

Beyond the kernel module, kqemu requires support from the QEMU userspace emulator to take advantage of the kqemu kernel hooks.

How is it different from kvm?

Unlike kvm, kqemu has never been accepted in the upstream Linux kernel.

Also different from kvm is the fact that kqemu works on hardware that does not support CPU Virtualization Technology (VT extensions), see Intel VT and AMD-V.

When would I want to use kqemu?

If your CPU supports VT or you have access to hardware that supports VT, you have no need for kqemu, as kvm is a far more complete, better performing, fully supported, and more modern alternative. Otherwise, kqemu arguably may be useful on some legacy hardware without VT.

How do I know if my hardware supports VT?

Just run kvm-ok from a command line and it should tell you.

Why was support for kqemu dropped from Ubuntu?

Quite simply, the upstream QEMU community deprecated kqemu in favor of kvm.

The upstream qemu-0.11 release series (which was in Ubuntu 9.10) disabled kqemu in the build. And the upstream qemu-0.12 release series (which is in Ubuntu 10.04 LTS) actually removed all remnants of the kqemu hooks from the source.

Why did upstream QEMU drop support for kqemu?

This was thoroughly discussed on the upstream qemu-devel mailing list by the developers of QEMU, as well as many users. An open poll was conducted by QEMU upstream to gauge the usefulness of kqemu. (The Ubuntu Server Team also conducted a poll and held a discussion on the topic at UDS-Lucid in Dallas, Texas in November 2009.)

You can read the hundreds of messages, as well as the handful of bug reports, if you like, but there are two primary reasons:

1. kqemu has no active maintainer. Upstream is open to reconsidering kqemu support, if an active maintainer steps up, fixes the open issues, and commits to providing ongoing support.
2. kqemu code within QEMU actually conflicts or breaks KVM code paths (specifically some required for 64-bit KVM support).

What are my alternatives to kqemu in Ubuntu 9.10, Ubuntu 10.04 LTS, and beyond?

Ideally, you would have access to VT-capable hardware, and use qemu-kvm, leveraging its outstanding performance, security model, and support from the various communities responsible for delivering it to you in Ubuntu (including the upstream Linux kernel, QEMU development team, Ubuntu Server Community, and the Canonical Server Team).

We cannot stress this enough:

• KVM is absolutely your best option for enterprise-ready, production-critical, supported deployments of Virtualization stacks built upon Ubuntu Servers.

If, instead, you're looking for occasionally running non-critical virtual machines on your Ubuntu desktop, I would recommend VirtualBox (see the virtualbox-ose package in Ubuntu). VirtualBox provides decent performance on systems without VT, as well as a rather user-friendly interface. VirtualBox is currently in Ubuntu Universe, so it is supported on a best-effort basis by the Ubuntu Community and Canonical.

:-Dustin

Server Bug Zapping: Libvirt

Jamie Strandboge and I spent today working on Ubuntu Lucid's libvirt package.

We did a bit of testing of the libvirt 0.7.7 merge that Jamie has in his PPA, and we spent several hours triaging all of Ubuntu's libvirt bugs.

We managed to reduce the number of open bugs from 78 to 41 with a thorough testing of Lucid's libvirt package against the open bugs, a bit of duplicate matching, and some expiration of a few others.

I uploaded one libvirt fix to an issue that can be solved with the new upstart job. If we decide to upload 0.7.7 to Lucid, there's a few others that will be closed too. And if not, we can cherry pick a few commits.

Finally, if you can give us some help, try installing Jamie's libvirt 0.7.7 merge in Lucid and let us know how well it works for you, and if there are any regressions. Cheers!

:-Dustin

qemu-kvm daily builds, thanks Chuck!

Chuck Short (one of the unsung heroes of the Ubuntu Server) has been working hard to get daily builds from upstream source repositories into Ubuntu PPAs in Launchpad.

He recently added qemu-kvm to the list of daily built upstream projects. You can see Chuck's announcement here.

Thanks, Chuck!

:-Dustin

Ubuntu Virtualization Poll - Your Feedback Requested!

We're still a week away from releasing Ubuntu 9.10, which I'm sure will be a phenomenal server release, with huge strides in virtualization and cloud hosting. The Ubuntu Enterprise Cloud should be the most complete open source cloud hosting solution in the industry.

But we're also beginning to prepare for the Ubuntu Developer Summit in Dallas, Texas next month. At this summit, we will discuss our plans for Ubuntu Lucid Lynx, which will release in April 2010 as Ubuntu 10.04 LTS. This being an LTS release, UDS is incredibly important, as these decisions will affect the Ubuntu landscape for at least 5 years.

As your maintainer of Ubuntu's virtualization stack supported by Canonical, I'm pleased to invite you to provide feedback on virtualization in Ubuntu in this simple, brief, 6-question survey:

http://www.surveymonkey.com/s.aspx?sm=7GN1uktb6nVdlegKYdbeJg_3d_3d

We are eager to hear your feedback on a few particular questions about KVM, QEMU, Virsh, Virt-Manager, Xen, VirtualBox, OpenVZ, VMWare, Parallels, Amazon EC2, Eucalyptus, and other virtualization technologies.

Note: Nick Barcet will be conducting a much more comprehensive Ubuntu Server Survey in the near future. Stay tuned!

Thanks!
:-Dustin