Re: [Qemu-devel] [PATCH 1/3] qga: introduce guest-get-vcpus / guest-set-vcpus with stubs

[Laszlo Ersek <lersek@redhat.com>]

On 03/06/13 00:12, Eric Blake wrote:

> The old cpu_set HMP command "worked" in something like qemu 0.10, and
> was ripped out when we realized it didn't actually work in a way that
> was guaranteed to be safe to the guest.  Since then, the libvirt command
> has been a guaranteed failure on qemu, although it continues to work on
> xen (and since it has been several YEARS now of not working, people are
> laughing at qemu for not getting cpu hotplug working when xen has had it
> for so long).

Under xen there's a separate comms method for requesting this (dom0 side
massaging of a specific node in xenstore + xenstore watch in the guest
kernel on that node).

http://wiki.xen.org/wiki/XenBus
http://wiki.xen.org/wiki/Event_Channel_Internals

>> I'll have to test this in RHEL-6. If it doesn't work, I should check
>> why. If it does, I'll have to figure out if I should continue to work on
>> this.
> 
> Yes, PLEASE continue to work on this - having the guest agent as an
> alternative to ACPI has proven useful in other respects (for example, we
> wired up virDomainShutdownFlags() to let the user choose between
> guest-agent, ACPI, or hypervisor choice).

OK.

Laszlo