Kashyap Chamarthy <kcham...@redhat.com> writes:
> The intended functionality of QMP command `cpu-add` is replaced by
> `device_add` (and `query-hotpluggable-cpus`). So let's deprecate
> `cpu-add`.
>
> A complete example of vCPU hotplug with the recommended way, using
> `device_add`:
>
> (1) Launch QEMU as follows (note that the "maxcpus" is mandatory to
> allow vCPU hotplug):
>
> $ qemu-system-x86_64 -display none -no-user-config -m 2048 \
> -nodefaults -monitor stdio -machine pc,accel=kvm,usb=off \
> -smp 1,maxcpus=2 -cpu IvyBridge-IBRS \
> -blockdev
> node-name=node-Base,driver=qcow2,file.driver=file,file.filename=./base.qcow2 \
> -device virtio-blk,drive=node-Base,id=virtio0 -qmp
> unix:/tmp/qmp-sock,server,nowait
>
> (2) Run 'qmp-shell' (located in the source tree) to connect to the
> just-launched QEMU:
>
> $> ./qmp/qmp-shell -p -v /tmp/qmp-sock
> [...]
> (QEMU)
>
> (3) Check which socket is free to allow hotplugging a CPU:
>
> (QEMU) query-hotpluggable-cpus
> {
> "execute":"query-hotpluggable-cpus",
> "arguments":{
>
> }
> }
> {
> "return":[
> {
> "type":"IvyBridge-IBRS-x86_64-cpu",
> "vcpus-count":1,
> "props":{
> "socket-id":1,
> "core-id":0,
> "thread-id":0
> }
> },
> {
> "qom-path":"/machine/unattached/device[0]",
> "type":"IvyBridge-IBRS-x86_64-cpu",
> "vcpus-count":1,
> "props":{
> "socket-id":0,
> "core-id":0,
> "thread-id":0
> }
> }
> ]
> }
> (QEMU)
When I try this, JSON gets formatted slightly differently:
{
"execute": "query-hotpluggable-cpus",
"arguments": {}
}
{
"return": [
{
"type": "IvyBridge-IBRS-x86_64-cpu",
"vcpus-count": 1,
"props": {
"socket-id": 1,
"core-id": 0,
"thread-id": 0
}
},
{
"qom-path": "/machine/unattached/device[0]",
"type": "IvyBridge-IBRS-x86_64-cpu",
"vcpus-count": 1,
"props": {
"socket-id": 0,
"core-id": 0,
"thread-id": 0
}
}
]
}
How come?
>
> (4) We can see that socket 1 is free, so use `device_add` to hotplug
> "IvyBridge-IBRS-x86_64-cpu":
>
> (QEMU) device_add id=cpu-2 driver=IvyBridge-IBRS-x86_64-cpu socket-id=1
> core-id=0 thread-id=0
> {
> "execute": "device_add",
> "arguments": {
> "socket-id": 1,
> "driver": "IvyBridge-IBRS-x86_64-cpu",
> "id": "cpu-2",
> "core-id": 0,
> "thread-id": 0
> }
> }
> {
> "return": {}
> }
> (QEMU)
>
> (5) Optionally, run QMP `query-cpus-fast` for some details about the
> vCPUs.
Publishing this in a commit message is much better than not publishing
it. Still, can we find a better home somewhere under docs/?
> Suggested-by: Eduardo Habkost <ehabk...@redhat.com
> Signed-off-by: Kashyap Chamarthy <kcham...@redhat.com>
> ---
> Also shouldn't we update tests/cpu-plug-test.c to make it use
> `device_add`. Can take a stab at it, if you'd like me to.
Yes, please.
> ---
> qapi/misc.json | 6 +++++-
> qemu-deprecated.texi | 5 +++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/qapi/misc.json b/qapi/misc.json
> index d450cfef21..83bc9ad0ee 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -1104,7 +1104,11 @@
> ##
> # @cpu-add:
> #
> -# Adds CPU with specified ID
> +# Adds CPU with specified ID.
> +#
> +# Notes: This command is deprecated. The `device_add` command should be
> +# used instead. See the `query-hotpluggable-cpus` command for
> +# details.
> #
> # @id: ID of CPU to be created, valid values [0..max_cpus)
> #
Eduardo pointed out that query-hotpluggable-cpus's documentation is
lacking. Add a suitable TODO there?
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index 1b9c007f12..9c6d70d43a 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -155,6 +155,11 @@ The ``query-cpus'' command is replaced by the
> ``query-cpus-fast'' command.
> The ``arch'' output member of the ``query-cpus-fast'' command is
> replaced by the ``target'' output member.
>
> +@subsection cpu-add (since 3.1)
> +
> +The intended functionality of ``cpu-add'' command, which is the ability
> +to hot-plug vCPUs, can now be achieved by the ``device_add'' command.
> +
For me, "now" suggests device_add can achieve this since 3.1. Scratch
"now"?
> @section System emulator devices
>
> @subsection ivshmem (since 2.6.0)
