Ubuntu 14.04 KVM : how to offline/online vCPU cores on virtual machines

Here is how to online/offline vCPU via virsh qemu-comamnd

assume you already set up qemu-guest-agent.

KV host : Ubuntu14.04

VM : CentOS 6.6

on the KVM host

virsh # qemu-agent-command centos6-vm1 '{"execute":"guest-get-vcpus"}' {"return":[{"online":true,"can-offline":false,"logical-id":0},{"online":true,"can-offline":true,"logical-id":1},{"online":true,"can-offline":true,"logical-id":2},{"online":true,"can-offline":true,"logical-id":3},{"online":true,"can-offline":true,"logical-id":4},{"online":true,"can-offline":true,"logical-id":5},{"online":true,"can-offline":true,"logical-id":6},{"online":true,"can-offline":true,"logical-id":7}]}

offline logical-id 5

virsh # qemu-agent-command centos6-vm1 '{"execute":"guest-set-vcpus", "arguments" : { "vcpus" : [{"online":false, "can-offline":false,"logical-id":5}]}}' {"retur2n":1}

VM’s log ( dmesg )

CPU 5 is now offline

online logical id 5 again.

virsh # qemu-agent-command centos6-vm1 '{"execute":"guest-set-vcpus", "arguments" : { "vcpus" : [{"online":true," can-offline":false,"logical-id":5}]}}' {"return":1}

VM’s log

Booting Node 0 Processor 5 APIC 0x5 kvm-clock: cpu 5, msr 0:28356841, secondary cpu clock kvm-stealtime: cpu 5, msr 2834e880

offline multiple cores at one time.

virsh # qemu-agent-command centos6-vm1 '{"execute":"guest-set-vcpus", "arguments" : { "vcpus" : [{"online":false,"can-offline":false,"logical-id":5},{"online":false,"can-offline":false,"logical-id":6}]}}' {"return":2}