KVM = Kernel-based Virtual Machine


It seems that a sort of hypervisor is going to be added to the mainline Linux kernel. It has been dubbed KVM... as if KVM weren't already taken by "Keyboard, Video Mouse". In this case, KVM stands for Kernel-based Virtual Machine... and it only works in CPUs that have VT (Intel) or AMD-V/SVM (AMD) extensions via a module named kvm.ko... and will available upon the release of the 2.6.20 kernel.

How does it differ from other virtualization schemes? From the FAQ:

What is the difference between kvm and Xen?

Xen is an external hypervisor; it assumes control of the machine and divides resources among guests. On the other hand, kvm is part of Linux and uses the regular Linux scheduler and memory management. This means that kvm is much smaller and simpler to use.

On the other hand, Xen supports both full virtualization and a technique called paravirtualization, which allows better performance for modified guests. kvm does not at present support paravirtualization.

What is the difference between kvm and VMWare?

VMware is a proprietary product. kvm is Free Software released under the GPL.

What is the difference between kvm and QEMU?

Qemu uses emulation; kvm uses processor extensions for virtualization.

And now for the question everyone wants to ask:

What OSs can I run inside kvm VM?

We have tested Linux (32/64 bit) and Windows (32 bit). Others may or may not work. 64-bit Windows is known not to work. This will be fixed once qemu-0.8.3 is released and merged. Several Linux flavors are known to hang on Intel processors during startup. Workaround is to disable splashscreens in grub.

I wonder how long before this becomes part of all of the distributions... and how it might conflict with Xen???

kvm-external.pdf432.76 KB

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What is QEMU? (something

What is QEMU? (something tells me it's a dumb question:D)

Scott Dowdle's picture

Best answer... from wikipedia

What is QEMU?


Scott Dowdle's picture

KVM article with some benchmarks

Wondering how fast KVM is and how well it works? I ran across an article entitled Finally user-friendly virtualization for Linux which details installing Microsoft Windows XP under QEMU, kqemu, and KVM and compares all three to native machine performance. KVM performs quite well even in its first release.

If only KVM didn't require a relatively new CPU with built-in VT hardware.

Obligatory quote:

OK, so with Windows XP installed in no time, I had plenty of time left to do some simple benchmarks. Nothing comprehensive or scientific, I remind you, just a few quick tests so that you have rough idea how KVM works in practice. I've also included few other interesting cases, because it was easy to do. Once I had installed Windows OS, it could be run even under unmodified QEMU, no problem. And with a little additional effort I also compiled kqemu, QEMU accelerator module written by QEMU's original author, unfortunately a closed-source product. Finally, the choice of the applications that I ran has fallen to only two of them, PCMark2002 and Super PI (ver 1.1e) with the sole reason that I had numbers from those two applications from the times when I had Windows XP installed natively (but that was few months ago, and I have since deleted it). Before I forget, the tests were run on an Intel E6600 processor.

Scott Dowdle's picture

Virtualization coming out of the wood work?

Just learned of yet another virtualization product - Virtual Iron. Virtual Iron is a closed source, commercial product... but they do offer a free basic version (much like VMware). Only trouble is that I can't run it. Why? Because it requires the newer, high-end processors with VT technology.

Does anyone have a machine it'll run on? If so, it would be nice if someone could give a demo at a LUG meeting!

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