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Re: [Xen-users] SMP limits in 3.0

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] SMP limits in 3.0
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 4 Aug 2005 16:06:32 +0100
Cc: Alan Greenspan <alan@xxxxxxxxxxx>
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Didn't see a reply to this, so...

> What are the maximum number of virtual CPUs a domU can be configured with?

I'm not sure what the absolute maximum is but you can configure it above the 
number of physical CPUs in the system (if you really want ;-)

> Can the number of CPUs be changed dynamically once the domU is booted?

Yep, I believe there's CPU hotplug support in there.  You should be able to 
add / remove CPUs using an xm command, although I've not tried it.

> If so, can it be changed from within the domU or only from the management
> interface?

Probably both, although again I've not checked.  If it hooks into the standard 
Linux hotplug CPU patch, the guest can do it at its discretion.

> > Will there be min/max settings for CPUs ala RAM?  

For number of CPUs?  That'd probably be sensible, guests certainly won't be 
able to exceed a given allocation.  You'll also be able to tweak the 
scheduling parameters to determine how the virtual CPUs are scheduled, i.e. 
how "good" the CPUs the domain sees are.

Cheers,
Mark

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