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Re: [Xen-users] reboot needed to increase vcpus??

On Thu, 2012-04-19 at 21:36 +0100, Shane Johnson wrote:
> Dan,
> From what I have seen, it depends on if you are using PV or HVM
> DomU's.  PV you can use the xm vcpu-set {domain} {#vcpus} and you
> should be good to go.

I'm not actually 100% sure but you might also need to configure the
guest (using "maxvcpus" and "vcpus") to have some spare "unplugged" CPU
slots at boot time such that you can dynamically increase them. e..g 
        vcpus = 2
        maxvcpus = 8
would boot with 2 vcpus initially but give you space to increase this to
anything up to 8 (or down to 1).

>   HVM you can use the same command but the Guest will have to be
> rebooted in order to see the update.

In HVM it depends a bit on the guest, if you do the maxvcpus thing then
you may well be able to plug more at run time and have them get picked

AFAIK this all depends on the level of the guest kernel's support for
physical CPU hotplug and ACPI. For example with some you can hot plug
but not hotunplug a CPU.

> If you are using a updated xen the command is xl I believe (I am on
> Debian squeeze for my host so the commands above are what I use)


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