On Fri, Jan 21, 2011 at 5:04 AM, Daniel P. Berrange <berrange(a)redhat.com> wrote:
That is correct. The live memory adjustment for KVM/QEMU via
libvirt is ballooning, not memory hotplug. Likewise for Xen
and VMWare. Real memory hotplug is a future RFE.
> I've read some stuff here:
>
http://www.linux-kvm.org/page/CPUHotPlug
Yep, CPU hotplug is available for KVM/libvirt, but support among
common guest OS is flakey. It doesn't work at all for Windows,
and for Linux only hotplug works, but not unplug. Xen however
did allow hot-unplug because it was using a different mechanism
IIUC.
For KVM, HDD hotplug already works for virtio disks, or SCSI
disks, or USB disks. It doesn't work for IDE disks. For Xen
hotplug works for xen paravirt disks.
For KVM, NIC hotplug also works, and in general any kind of
emulated PCI device can be hotplugged. For Xen, again their
xen paravirt NICs could be hotplugged.
So, in practical terms,
RAM "extension" is done by ballooning
CPU hotplugging is possible but not unplugging.
And HDD hotplugging is possible...
I read a thread (2008) that offered a patch on this ACPI technique for
RAM HotPlugging. Check it out:
http://www.spinics.net/lists/kvm/msg27395.html
CPU UnPlugging is not considered as a needed feature is it?
http://www.linux-kvm.org/page/CPUHotPlug
"Hot-unplug does not work, and actually, does not even make that much sense."