On Wed, Sep 26, 2018 at 05:24:27PM +0200, Igor Mammedov wrote:
> On Tue, 25 Sep 2018 18:02:48 +0200
> Kashyap Chamarthy <kcham...@redhat.com> wrote:
[...]
> > +(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
> >
> all options beside of -smp and -qmp are not relevant here and mostly masking
> parts that matter, I'd simplify it as much as possible:
> qemu-system-x86_64 -smp 1,maxcpus=2 -qmp unix:/tmp/qmp-sock,server,nowait
> ...
Sure, I can cut it down. (That specific command-line is what I normally
use when playing with the QEMU Block Layer.)
> Also example only covers x86 target, but there are ppc target with
> spapr machine (add/del) and s390 target (add only). probably should be
> mentioned here as well
I'll probably just mention about PPC and s390. But adding examples for
them too is a bit redundant.
> In addition one could coldplug cpus the same way as other devices
> using -device CLI option.
Good point, I'll mention it.
> > +(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::
> >
> may be: which cpus are possible to plug (an entry with qom-path
> property describes an existing cpu)
As a user of QMP, I don't find that phrasing clear as well, I'm afraid.
Wonder if there's a way better way to tell what's happening here.
[...]
> > +(4) We can see that socket 1 is free, so use `device_add` to hotplug
> >
> ... and 'arguments' provide a list of property/value pairs to create
> corresponding cpu.
Noted.
[...]
> > +(5) Optionally, run QMP `query-cpus-fast` for some details about the
> > + vCPUs::
> >
> I'd replace it with another query-hotpluggable-cpus call
Will do.
> > +
[...]
> > +vCPU hot-unplug
> > +---------------
> > +
> > +From the 'qmp-shell', invoke the QMP ``device_del`` command::
> > +
> > + (QEMU) device_del id=cpu-2
> > + {
> > + "execute": "device_del",
> > + "arguments": {
> > + "id": "cpu-2"
> > + }
> > + }
> > + {
> > + "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
> > + Interupt (SCI) and calls the ACPI handler for the affected vCPU
> > + device. Then the guest kernel will bring the vCPU offline and tells
> > + QEMU to unplug it.
> s/tells/tell/
Will fix.
Thanks for the review, Igor!
--
/kashyap
