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I run VirtualBox 3.1 on Ubuntu with a Win XP guest. I have noticed to my surprise that when I pause the VM (its screen grays out) VirtualBox continues using 15-20% of the host's CPU.

Is this normal behavior?

Is there a way to avoid it? (Without saving the state of the VM and exiting VirtualBox.)

Thanks for any insights!

~lara

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2 Answers

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In order to lessen VirtualBox CPU usage at all times, resort to this weird hack.

Create a new virtual machine and do not install an operating system to it. Tell VirtualBox it will run DOS and give it the absolute minimum resources. Do not install an O/S. Run it, let it error out on boot and minimize it.

While running your real O/S in a second VM, you will see your idle Virtualbox CPU utilization drop to 3-5%.

Idea from jed4czar: http://ubuntuforums.org/showthread.php?s=58e862a814e65eb96f8fe8389b615366&t=838073&page=2

EDIT: To answer your questions directly

why does Virtualbox use 15-20% CPU when VM is paused?

It is a bug. It is always using 15-20% more CPU than it needs to, when any one VM is up, unless the hack provided is used.

Is there a way to avoid it?

See hack above.

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nice to know, that vbox allocates possibliy used cpu-sources on startup – Diskilla Apr 16 '10 at 12:06
very nice, many thanks! – laramichaels Apr 16 '10 at 19:55
You're welcome, and thanks for accepting my answer. Many don't bother, but a high acceptance rate is a mark of good behavior on the Trilogy websites. – kmarsh Apr 19 '10 at 12:17
up vote 0 down vote

I experienced this VirtualBox issue on a 2-cpu P4 machine with 3gigs ram running CentOS 5.5 host.

I did not experience this issue on an i720 8cpu machine with 8 gigs running 64-bit Win7. I ran 3 VMWare virtual machines plus the VirtualBox, all with 2-gigs memory, and had no CPU issues whatsoever.

This suggests either running on a "smallish" machine or on a Linux host is the problem.

Your solution worked well, thanks.

I note that these earlier posts are a year old, and my VirtualBox is the most recent Version 4.0.4, so Oracle has not fixed this bug yet.

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I would expect that this performance penalty is associated with the face that newer CPUs have VT-x and similar to allow hardware assisted virtualisation which would mean that the VirtualBox program is not doing the work and therefore lower CPU usage. A P4 would likely not have the VT-x technology and so would have to translate system calls via software and use more CPU as a result. – Mokubai Mar 24 '11 at 22:38

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