Re: [Xen-users] Xen 3.1 64bit / 32bit domU performance

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I'm going to install Xen on a new 64bit capable machine with 16GB RAM and
> two quad-core Xeon. The domU's are (for migration issues) all 32bit PAE PV.
> My question is, should I install a 32bit PAE (which i prefer) or a 64bit
> Xen? Are there any known performance issues running 32bit PAE PV's on a
> 64bit Xen? It's really unlikely that the machine will be upgraded to more
> than 16GB.

AFAIK, 32-bit PAE PV guests should perform well on 64-bit Xen - if anything, 
they might well be better performing than 64-bit guests.  This is because 
protecting Xen from 64-bit guests incurs a higher performance penalty than 
for protecting it from 32-bit guests.

By the way, I don't think it's possible to suspend / resume or live migrate 
32-bit PV guests on a 64-bit Xen yet.  I guess that'll be in a future 
release.  Also, I understand that pre-3.1 32-bit kernels won't run on vanilla 
3.1, but subsequent patches that are in the -unstable tree provide 
compatibility for these older kernel builds too.

HVM guests are a separate issue, by the way, as their memory etc is handled 
differently.

> And btw. does someone know if the 32bit PAE PV domU's memory limit is also
> at 16GB or smaller (well, assuming more physical RAM)?

I'm not sure on this.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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