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cyberfishee 12-12-2007 05:38 PM

[Xen] 64-bit DomU on 32-bit Dom0?
Is it possible to run a 64-bit DomU(guest) on a 32-bit Dom0(host)? Both Linux. I know it is possible in VMware (tried it myself), but is it possible on Xen? My google search has been fruitless.

Thank you

tecnalb 12-12-2007 09:55 PM

on rhel5 xen a 32bit host can only run a 32bit para-vm guest. the docs indicate that architecture must remain similar.

cyberfishee 12-12-2007 09:58 PM

thank you for your reply,

but is that redhat specific? I'm using debian/ubuntu here.

tecnalb 12-12-2007 10:16 PM

Well, I know they do tune some things, like preventing vm support on non-pae CPUS (like my laptop) in rhel. Xen supports that in fedora, but
they disabled (requires kernel recompile) in production rhel5.

Here is the marketing page. Maybe it will help you dig down a bit

cyberfishee 12-12-2007 11:21 PM

yeah it does say it's not possible in rhel, but I don't know if that's a limitation of Xen or rhel. I have never used rhel, too.

tecnalb 12-13-2007 04:01 PM

I did find this:

Physical Address Extension (PAE) allows 32-bit servers to address more than 4 GB memory, and 64-bit addressing for up to 8 TB of memory. I assume you've looked at, right?

cyberfishee 12-13-2007 05:34 PM

Thank you for your help. Yes I did look at The amount of addressable memory is not my concern here. I only have 2G of ram in total. I want to go to 64-bit because I am writing some computationally intensive program that makes extensive use of 64-bit data types (a chess AI in this case), and it would benefit from 64-bit wide registers (I saw a 0.7x speed increase running it in VMware 64-bit, but would rather use Xen).

tecnalb 12-13-2007 08:41 PM

You have peaked my interest so I may try to load a 64bit para-vm on one of my 32bit servers and see if it runs. I do know that on 2GB or ram, the host is somewhat slow with just Dom0 and one 32bit guest, but that may not matter in your case.

cyberfishee 12-13-2007 10:00 PM

thanks =) well in my case I think 2GB is more than enough (no swapping at all).

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