[Qemu-devel] VCPU Hot-Unplug Feature

[Qemu-devel] VCPU Hot-Unplug Feature

[Fahri Cihan Demirci]

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

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

[Alexandre DERUMIER]

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 

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

[Fahri Cihan Demirci]

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 

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

[Eduardo Otubo]

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On Mon, May 04, 2015 at 09=34=21PM +0300, Fahri Cihan Demirci wrote:
> 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.

We're very interested in having this feature upstream as well. As Fahri
stated above, I also would like to offer help to get it pushed.

What's the current status?

Regards,

> 
> 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 
> 

-- 
Eduardo Otubo
ProfitBricks GmbH

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