Re: [Xen-users] Xen 3.1 - 32 vs 64 bit hypervisor

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> I've been experimenting with Xen 3.1.
>
> My requirements are to run lots 32 bit paravirt domains on large
> memory hosts (8GB or more).
>
> Previously I've used a 32 bit Xen with PAE hypervisor which works
> well.  However I seen from the announcement that you can use a 64 bit
> hypervisor and still run 32 bit PAE domains.  I've tried this and it
> works as advertised!

Awesome :-)

> What I'm wondering is, will it be best for me to run a 32 bit PAE Xen
> hypervisor or a 64 bit hypervisor?  What is the tradeoff between the
> two? Which is likely to be more efficient and which more stable?

Stability-wise, 32-on-64 is a new feature so it will have received less real 
world abuse testing.  There may be teething troubles.  Performance-wise...  
Again, the combination is less tested, so it's not inconceivable that there 
will be teething troubles.

That said, in principle it ought to be alright.  32-on-64 even fully supports 
glibc's TLS, which even 32-on-32 doesn't (this is because of slightly arcane 
implementation details in x86.  Really.  The mind boggles.).

If you're running a 64-bit Xen, I think you also have the potential to run 
64-bit paravirt guests, and 64-bit HVM guests in addition to all the stuff 
you could run on 32-bit Xen.

At some point it should be possible to run a 32-bit dom0, but I'm not sure if 
that's allowed yet.

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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