I have a 64-bit Virtualbox guest running Gentoo Linux (amd64) and it is currently hosted on a 32-bit Gentoo laptop.

I've noticed that the performance of the VM is very slow compared to the performance of the 32-bit host itself. Also when I compare with another 32-bit Linux VM running on the same host, performance is significantly less on the 64-bit VM.

I know that running a 64-bit VM on a 32-bit host does incur some performance penalties for the VM, but does anyone have any deeper knowledge of how large a penalty one might expect in this scenario, roughly speaking? Is a 10% slowdown something to expect, or should it be a slowdown in the 90% range (running at 1/10 the normal speed)?

Or to phrase it in another way: would it be reasonable to expect that the performance improvement for the 64-bit VM increases so much that it is worth reinstalling the host machine to run 64-bit Gentoo instead? I'm currently seriously considering that upgrade, but am curious about other peoples experience of the current scenario.

I am aware that the host OS will require more RAM when running in 64-bit, but that's OK for me. Also, I do know that one usually don't run a 64-bit VM on a 32-bit server (I'm surprised I even got the VM started in the first place) but things turned out that way when I tried to future proof the VM I was setting up and decided to make it 64-bit anyway.


I have no numbers to provide but given the fact VirtualBox doesn't support such a configuration unless explicitly requested (see 64 bit guests - Virtual Box Manual), I would expect a significant performance penalty.


Virtualization systems usually gain significant performance by exposing host hardware to guests system as directly as possible with minimal translation, and usually do that by installing specialized drivers on guest system, as VirtualBox Addon Packs do. The problem with your setup is that such an exposure is not possible because of different hardware setups, which means a lot of translation will be necessary, which in turn will not only mean losing the performance boost, but also slowing down even more because of excessive translation (compared to your host).

Having said that, I'm suprised you got it working at all in the first place with VirtualBox.

Just as a note: you do have set the Virtualization Enable bit in your BIOS right ?

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