On Fri, Jan 21, 2011 at 12:34:29PM -0600, Renich Bon Ciric wrote: > On Fri, Jan 21, 2011 at 5:04 AM, Daniel P. Berrange <berrange@xxxxxxxxxx> 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 NB, you can't ever extend RAM beyond initial boot amount with ballooning. It merely lets you adjust it to any value below the initial boot amount, and back up. > 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 Yep, not merged though. It will likely come eventually but for now the focus has been in other areas of the RAM subsystem like transparent huge pages and KSM page merging which have a far greater benefit. > > 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." I wouldn't neccessarily agree with the statement on that page. I think it is perfectly valid to be able to want to unplug CPUs. If you have a 4 CPU guest on a 4 CPU host, and need to migrate the guest to a 2 CPU host, then it could well be a better idea to unplug 2 of the guest CPUs than leave it overcommitted. Thus I expect someone will make hot-unplug work eventually Daniel _______________________________________________ cloud mailing list cloud@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/cloud
