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)
(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.
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.
---
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)
#
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.
+
@section System emulator devices
@subsection ivshmem (since 2.6.0)
--
2.17.1
