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Re: [Xen-users] 32 bit versus 64 bit

To: Mathias Diehl <md@xxxxxxxxxxxxx>
Subject: Re: [Xen-users] 32 bit versus 64 bit
From: Nicholas Lee <emptysands@xxxxxxxxx>
Date: Sat, 26 Nov 2005 10:58:50 +1300
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Might be useful to make a FAQ item for this.

On 11/26/05, Mathias Diehl <md@xxxxxxxxxxxxx> wrote:
> Hi List,
> because I'm still quite new to Linux please kindly advise about hardware.
> I need a new server and need to understand how xen will handle 32 / 64 bit 
> systems.

With Xen you can either have 32bit kernels or 64 bit kernels, not
both. If the Dom0 kernel is 64 bit, then xend needs 64bit python to
talk to the 64 bit xen hypervisor.

64bit kernel can otherwise run either mixed, 32, or 64 bit userland.

> Main contraint is a 32 software to be running on a domU.
> So - do I still need to run XEN on a 32bit system or will my software (java 
> application) also run on a 64bit system?. I noticed that I will not be able 
> to run a 32 domU on a 64 dom0

64 bit will give you a definite bonus in performance.  I've seen two
times speed jump in some tests for full 64 bit.  Even 32bit userland
gets a big boost from the extra registers with a 64bit kernel.

I'd suggest running a 64bit domU kernel with a 32 bit userland.

Nicholas Lee
gpg 8072 4F86 EDCD 4FC1 18EF  5BDD 07B0 9597 6D58 D70C

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