Re: About the change of a VM's vcpu count in runtime?

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On 06/01/2013 03:16 PM, Dennis Chen wrote:
On 05/29/2013 04:28 AM, Eric Blake wrote:
On 05/28/2013 02:24 PM, Eric Blake wrote:

So the question is: is there any method I can't find yet to change the
vcpu count of a running vm dynamically?
Wait for newer qemu and libvirt, or else pitch in and help write patches.
You might not have to wait that long - if you could help test these
patches, it would be appreciated:

https://www.redhat.com/archives/libvir-list/2013-May/msg01857.html

Hi,

After apply the patch, I've made a test. The testing environment as:

virsh # version
Compiled against library: libvirt 1.0.5
Using library: libvirt 1.0.5
Using API: QEMU 1.0.5
Running hypervisor: QEMU 1.5.0

The xml piece of the vm domain:
    <channel type='unix'>
<source mode='bind' path='/var/lib/libvirt/qemu/f16x86_64.agent'/>
        <target type='virtio' name='org.qemu.guest_agent.0'/>
    </channel>

the network connection between the vm and host is ok.

Also I installed the qemu-guest-agent in the guest os:
[root@localhost ~]#rpm -qa | grep qemu-guest
qemu-guest-agent-0.12.1.2-2.355.el6.i686

An error happened when I try to offline a guest vcpu in virsh:
virsh # setguestvcpu 8  1 --offline
error: Guest agent is not responding: Guest agent not available for now

Is there some step I missed before I invoke the 'setguestvcpu' command in virsh or I need to write a program to hot-plug/unplug the vcpu with the help of the new API introduced by this patch? Thanks!

BRs,
Dennis

update after investigation, I need to start up the 'qemu-guest-agent' daemon in the guest (https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/qemu-ga.html):
[root@localhost ~]#qemu-ga

After that, I tried the command again:
virsh # setguestvcpu 8 1 --offline
error: internal error unable to execute QEMU agent command 'guest-set-vcpus': The command guest-set-vcpus has not been found

I think the communication between monitor and guest is ok, because below command is OK:
virsh # shutdown 8 --mode agent
Domain 8 is being shutdown

VM shutdown after this command. Also, I double checked the src/qemu/qemu_agent.c, and I can find the 2 functions:
qemuAgentGetVCPUs() and qemuAgentSetVCPUs()

Another,
virsh # qemu-agent-command 9 '{"execute":"cpu-add","arguments":{"id":2}}'
{"error":{"class":"CommandNotFound","desc":"The command cpu-add has not been found","data":{"name":"cpu-add"}}}

Seems the guest agent can't find vcpu hot-plug/unplug command, the qemu I am using is 1.5.0, does it need some patches to handle this or something I still missed?

BRs,
Dennis

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