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[Qemu-devel] [PATCH] Deprecate QMP `cpu-add`

Kashyap Chamarthy posted 1 patch 7 years, 1 month ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20180920114406.20818-1-kchamart@redhat.com
Test docker-clang@ubuntu failed
Test checkpatch passed
qapi/misc.json       | 6 +++++-
qemu-deprecated.texi | 5 +++++
2 files changed, 10 insertions(+), 1 deletion(-)
[Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Kashyap Chamarthy 7 years, 1 month ago 
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 <ehabkost@redhat.com
Signed-off-by: Kashyap Chamarthy <kchamart@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
Re: [Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Markus Armbruster 7 years, 1 month ago 
Kashyap Chamarthy <kchamart@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 <ehabkost@redhat.com
> Signed-off-by: Kashyap Chamarthy <kchamart@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)
Re: [Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Kashyap Chamarthy 7 years, 1 month ago 
On Thu, Sep 20, 2018 at 02:27:02PM +0200, Markus Armbruster wrote:
> Kashyap Chamarthy <kchamart@redhat.com> writes:

[...]

> 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?

You caught me :-).  I actually get the same as you well.  But I fudged
the output by running it through:
https://jsonformatter.curiousconcept.com/ with "2 Space Tab", but it
doesn't make any difference.  

So I'll actually retain the original raw output from 'qmp-shell'.

> > (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/?

Good point.  I'll make an 'cpu-hotplug.rst' in docs/ and submit it
as a patch in v2.  Hope that's okay with you.

[...]

> > ---
> > 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.

Igor was saying on IRC that we can fix the test when we _actually_ do
the deprecation.  So I'll make a TODO (and won't forget) to make it as a
separate patch after we deprecate this.

[...]

> >  # @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?

Yes, will do.

> > 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"?

Yes, will do.

Thanks for the quick review!

-- 
/kashyap
Re: [Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Eduardo Habkost 7 years, 1 month ago 
On Thu, Sep 20, 2018 at 02:27:02PM +0200, Markus Armbruster wrote:
> Kashyap Chamarthy <kchamart@redhat.com> writes:
[...]
> > ---
> >  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?

Yes, please.

> 
> > 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"?

Agreed.

I would also try to write a shorter and simpler sentence, and
mention query-hotpluggable-cpus.  e.g.:

  The ``device_add'' command should be used for hotplugging VCPUs
  instead of ``cpu-add''.  See the documentation of the
  ``query-hotpluggable-cpus'' command for additional details.



> 
> >  @section System emulator devices
> >  
> >  @subsection ivshmem (since 2.6.0)

-- 
Eduardo
Re: [Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Markus Armbruster 7 years, 1 month ago 
Eduardo Habkost <ehabkost@redhat.com> writes:

> On Thu, Sep 20, 2018 at 02:27:02PM +0200, Markus Armbruster wrote:
>> Kashyap Chamarthy <kchamart@redhat.com> writes:
> [...]
>> > ---
>> >  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?
>
> Yes, please.
>
>> 
>> > 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"?
>
> Agreed.
>
> I would also try to write a shorter and simpler sentence, and
> mention query-hotpluggable-cpus.  e.g.:
>
>   The ``device_add'' command should be used for hotplugging VCPUs
>   instead of ``cpu-add''.  See the documentation of the
>   ``query-hotpluggable-cpus'' command for additional details.

Perhaps even

    Use ``device_add'' for hotplugging VCPUs instead of ``cpu-add''.
    See documentation of ``query-hotpluggable-cpus'' for additional
    details.

>
>
>
>> 
>> >  @section System emulator devices
>> >  
>> >  @subsection ivshmem (since 2.6.0)
Re: [Qemu-devel] [PATCH] Deprecate QMP `cpu-add`
Posted by Eduardo Habkost 7 years, 1 month ago 
On Fri, Sep 21, 2018 at 08:30:54AM +0200, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > On Thu, Sep 20, 2018 at 02:27:02PM +0200, Markus Armbruster wrote:
> >> Kashyap Chamarthy <kchamart@redhat.com> writes:
> > [...]
> >> > ---
> >> >  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?
> >
> > Yes, please.
> >
> >> 
> >> > 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"?
> >
> > Agreed.
> >
> > I would also try to write a shorter and simpler sentence, and
> > mention query-hotpluggable-cpus.  e.g.:
> >
> >   The ``device_add'' command should be used for hotplugging VCPUs
> >   instead of ``cpu-add''.  See the documentation of the
> >   ``query-hotpluggable-cpus'' command for additional details.
> 
> Perhaps even
> 
>     Use ``device_add'' for hotplugging VCPUs instead of ``cpu-add''.
>     See documentation of ``query-hotpluggable-cpus'' for additional
>     details.

Nice, that's even more straightforward and simple.

-- 
Eduardo

Patchew 2.1-devel-b67e4c2

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