cpu hot-add doesn't work with upstream qemu 1.5.50

[chandrashekar shastri]

cpu hot-add doesn't work with upstream qemu 1.5.50. When we add the cpu [through QMP] it throws error as " {"error": {"class": "GenericError", "desc": "Unable to add CPU: 2, max allowed: 1"}} ", when we have booted the guest with two cpus.

Host Kernel Version: 3.10.0-rc5+

Libvirt Version: 1.0.6

Qemu Version: 1.5.50

Guest Kernel : 2.6.32-358.6.1.el6.x86_64

Steps to Reproduce :

Boot the guest with : qemu-system-x86_64 -drive file='/home/images/vm1.qcow2',format=qcow2,cache=none,boot=on -m 2048 -smp 2,cores=2,threads=1,sockets=1 -qmp tcp:localhost:4444,server -monitor stdio -enable-kvm

Start the telnet localhost 4444 on another shell

verify that there are two cpus :

I verified through HMP
(qemu) info cpus
* CPU #0: pc=0x000000000000f081 thread_id=2034
  CPU #1: pc=0x00000000000f6497 (halted) thread_id=2031

Hot add the CPU using the below command in QMP:

{ "execute": "cpu-add", "arguments": { "id": 2 } }
{"error": {"class": "GenericError", "desc": "Unable to add CPU: 2, max allowed: 1"}}

Notes:
--------
1. By default [without specifying the no of cpu], the guest boots up with 1 cpu, when we try to add one more cpu, below is the error:

{ "execute": "cpu-add", "arguments": { "id": 1 } }
{"error": {"class": "GenericError", "desc": "Unable to add CPU: 1, max allowed: 0"}}

2. This issue is seen with or without enabling the KVM [i.e booting the guest without -enable-kvm option]

[Paolo Bonzini (bonzini)]

You need to specify "-smp maxcpus=N" on the command-line, for example "-smp cpus=2,maxcpus=4" will start the VM with 2 CPUs and let you add 2 more. Also, the argument to cpu-add is zero-based, so the range is 0..(maxcpus-1).

[chandrashekar shastri (cshastri)]

Hi Bonzini,

Thanks, cpu hot-plug is working.
Could you please help me with cpu hot-unplug It is working.

Thanks,
chandrashekar

On 06/27/2013 01:19 PM, Paolo Bonzini wrote:
> You need to specify "-smp maxcpus=N" on the command-line, for example
> "-smp cpus=2,maxcpus=4" will start the VM with 2 CPUs and let you add 2
> more. Also, the argument to cpu-add is zero-based, so the range is
> 0..(maxcpus-1).
>
> ** Changed in: qemu
> Status: New => Invalid
>

[Paolo Bonzini (bonzini)]

Il 27/06/2013 11:03, chandrashekar shastri ha scritto:
> Hi Bonzini,
>
> Thanks, cpu hot-plug is working.
> Could you please help me with cpu hot-unplug It is working.

It is not implemented yet.

Paolo

[chandrashekar shastri (cshastri)]

Ok. Thanks.

On 06/27/2013 02:39 PM, Paolo Bonzini wrote:
> Il 27/06/2013 11:03, chandrashekar shastri ha scritto:
>> Hi Bonzini,
>>
>> Thanks, cpu hot-plug is working.
>> Could you please help me with cpu hot-unplug It is working.
> It is not implemented yet.
>
> Paolo
>