bda8c24cb5
The example of how to do vCPU hotplug and hot-unlpug in the cpu-hotplug documentation no longer works, because the way we allocate socket-id and core-id to CPUs by default has changed at some point. The output also no longer matches what current QEMU produces in some more cosmetic ways. Update the example to match current QEMU. The differences are: * the second CPU is now socket-id=0 core-id=1, not socket-id=1 core-id=0 * the order of fields in QMP responses is now in alphabetical order * the "arch" member is no longer present in the query-cpus-fast output (it was removed in QEMU 6.0) Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Acked-by: Igor Mammedov <imammedo@redhat.com> Message-id: 20241010131800.3210161-1-peter.maydell@linaro.org Message-id: 20240819144303.37852-1-peter.maydell@linaro.org
141 lines
4.0 KiB
ReStructuredText
141 lines
4.0 KiB
ReStructuredText
===================
|
|
Virtual CPU hotplug
|
|
===================
|
|
|
|
A complete example of vCPU hotplug (and hot-unplug) using QMP
|
|
``device_add`` and ``device_del``.
|
|
|
|
vCPU hotplug
|
|
------------
|
|
|
|
(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 \
|
|
-qmp unix:/tmp/qmp-sock,server=on,wait=off
|
|
|
|
(2) Run 'qmp-shell' (located in the source tree, under: "scripts/qmp/)
|
|
to connect to the just-launched QEMU::
|
|
|
|
$> ./qmp-shell -p -v /tmp/qmp-sock
|
|
[...]
|
|
(QEMU)
|
|
|
|
(3) Find out which CPU types could be plugged, and into which sockets::
|
|
|
|
(QEMU) query-hotpluggable-cpus
|
|
{
|
|
"execute": "query-hotpluggable-cpus",
|
|
"arguments": {}
|
|
}
|
|
{
|
|
"return": [
|
|
{
|
|
"props": {
|
|
"core-id": 1,
|
|
"socket-id": 0,
|
|
"thread-id": 0
|
|
},
|
|
"type": "IvyBridge-IBRS-x86_64-cpu",
|
|
"vcpus-count": 1
|
|
},
|
|
{
|
|
"props": {
|
|
"core-id": 0,
|
|
"socket-id": 0,
|
|
"thread-id": 0
|
|
},
|
|
"qom-path": "/machine/unattached/device[0]",
|
|
"type": "IvyBridge-IBRS-x86_64-cpu",
|
|
"vcpus-count": 1
|
|
}
|
|
]
|
|
}
|
|
(QEMU)
|
|
|
|
(4) The ``query-hotpluggable-cpus`` command returns an object for CPUs
|
|
that are present (containing a "qom-path" member) or which may be
|
|
hot-plugged (no "qom-path" member). From its output in step (3), we
|
|
can see that ``IvyBridge-IBRS-x86_64-cpu`` is present in socket 0 core 0,
|
|
while hot-plugging a CPU into socket 0 core 1 requires passing the listed
|
|
properties to QMP ``device_add``::
|
|
|
|
(QEMU) device_add id=cpu-2 driver=IvyBridge-IBRS-x86_64-cpu socket-id=0 core-id=1 thread-id=0
|
|
{
|
|
"execute": "device_add",
|
|
"arguments": {
|
|
"core-id": 1,
|
|
"driver": "IvyBridge-IBRS-x86_64-cpu",
|
|
"id": "cpu-2",
|
|
"socket-id": 0,
|
|
"thread-id": 0
|
|
}
|
|
}
|
|
{
|
|
"return": {}
|
|
}
|
|
(QEMU)
|
|
|
|
(5) Optionally, run QMP ``query-cpus-fast`` for some details about the
|
|
vCPUs::
|
|
|
|
(QEMU) query-cpus-fast
|
|
{
|
|
"arguments": {}
|
|
"execute": "query-cpus-fast",
|
|
}
|
|
{
|
|
"return": [
|
|
{
|
|
"cpu-index": 0,
|
|
"props": {
|
|
"core-id": 0,
|
|
"socket-id": 0,
|
|
"thread-id": 0
|
|
},
|
|
"qom-path": "/machine/unattached/device[0]",
|
|
"target": "x86_64",
|
|
"thread-id": 28957
|
|
},
|
|
{
|
|
"cpu-index": 1,
|
|
"props": {
|
|
"core-id": 1,
|
|
"socket-id": 0,
|
|
"thread-id": 0
|
|
},
|
|
"qom-path": "/machine/peripheral/cpu-2",
|
|
"target": "x86_64",
|
|
"thread-id": 29095
|
|
}
|
|
]
|
|
}
|
|
(QEMU)
|
|
|
|
vCPU hot-unplug
|
|
---------------
|
|
|
|
From the 'qmp-shell', invoke the QMP ``device_del`` command::
|
|
|
|
(QEMU) device_del id=cpu-2
|
|
{
|
|
"arguments": {
|
|
"id": "cpu-2"
|
|
}
|
|
"execute": "device_del",
|
|
}
|
|
{
|
|
"return": {}
|
|
}
|
|
(QEMU)
|
|
|
|
.. note::
|
|
vCPU hot-unplug requires guest cooperation; so the ``device_del``
|
|
command above does not guarantee vCPU removal -- it's a "request to
|
|
unplug". At this point, the guest will get a System Control
|
|
Interrupt (SCI) and calls the ACPI handler for the affected vCPU
|
|
device. Then the guest kernel will bring the vCPU offline and tell
|
|
QEMU to unplug it.
|