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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.

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migrated from serverfault.com Nov 11 '11 at 16:57

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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.

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