Running Linux VM inside Windows VM is very slow

[Krzysztof Lichota]

I am running Windows XP (SP3) virtual machine on Linux (Ubuntu 8.04-derived distro) host.

Inside this VM I have installed VirtualBox 3.0.12 and created VM for Linux guest (again Ubuntu 8.04-derived distro).

When I try to run this nested VM, it runs very slow (see attached screenshot), for example cleaning 65 KB dentry cache (which is instant on bare hardware or in one-level VM) takes ~18 seconds, checking available memory takes over 15 minutes. I wasn't able to boot the system in full, it just takes too long.

Processor is 100% used inside Windows VM when running VirtualBox.

I have also tested VirtualBox 3.1.2 running inside Windows VM, it is the same.

I have checked other distro (Damn Small Linux) and it also cannot boot, probably for the same reason (cannot check if it does anything as it does not display messages during boot).

I have tried to run Windows VM using Vmware Server 2 and run VirtualBox inside - it does not have performance hit (but the VirtualBox inside reports problem and quits), so it is possible to run with adequate performance on my hardware (Pentium Dual-core without VT-X).

[Krzysztof Lichota]

VBox log of outer VM (Windows guest on Linux guest)

[Krzysztof Lichota]

VBox log of inner VM (Linux VM running inside Windows host)

[Krzysztof Lichota]

Screenshot of Windows VM showing poor performance on Linux VM inside

[Krzysztof Lichota]

Forgot to mention - I have tried first without VirtualBox Guest additions, then installed Additions in hope that it will improve performance - it didn't.

[Sander van Leeuwen]

First of all your CPU is really slow and second we don't support nested VMs with software virtualization.

The only real option is VT-x or AMD-V combined with nested paging. We have no plans to change this. Too much work for very questionable benefits.