Re: [Qemu-devel] VCPU Hot-Unplug Feature

[Fahri Cihan Demirci <cihand@skyatlas.com>]

Hello Alexandre,

Thank you for your response. I came upon that patch on the Libvirt mailing list, too. However, the following comment makes me think that it's not likely to be merged:

https://www.redhat.com/archives/libvir-list/2015-February/msg00415.html

Also, later in the thread, the author of the patch seems to confirm that the plan for hotplug in QEMU is not compatible with that patch:

https://www.redhat.com/archives/libvir-list/2015-March/msg01169.html

So, I think Libvirt developers have decided to wait until there is a generalized groundwork for VCPU hot-unplug in the QEMU code base. That's why I decided to inquire and offer help for QEMU developers, since the ball seems to be in their court now.

Thanks a lot for your time.


On Mon, May 04, 2015 at 07:49:08PM +0200, Alexandre DERUMIER wrote:
> Hi,
> 
> they are a lot of patches sent on the mailing list recently,
> 
> cpu hotplug|unplug with device_add|del
> 
> https://www.redhat.com/archives/libvir-list/2015-February/msg00084.html
> 
> 
> 
> ----- Mail original -----
> De: "Fahri Cihan Demirci" <cihand@skyatlas.com>
> À: "qemu-devel" <qemu-devel@nongnu.org>
> Envoyé: Lundi 4 Mai 2015 18:24:43
> Objet: [Qemu-devel] VCPU Hot-Unplug Feature
> 
> Hello, 
> 
> We are interested in being able to remove a VCPU from an active Libvirt domain running under QEMU/KVM. However, currently that does not seem to be possible because QEMU does not provide an interface for hot-unplugging a VCPU. The corresponding feature page [1] on the QEMU wiki mentions the cpu-add interface and the generalized device add/del interface. So, my question is, is there someone working on a cpu-remove interface or making progress in the generalized device add/del interface to hot-unplug VCPUS? If you are in any way interested in or planning such a feature, we may provide feedback, testing or help in the development effort. Any other input, guidance or corrections would be also most welcome. Thank you. 
> 
> [1] http://wiki.qemu.org/Features/CPUHotplug 
> 
> 
> Best regards, 
> Fahri Cihan Demirci