KVM : CPU hotplug ( fail ! )

KVM host

# uname -ri 3.2.0-29-generic x86_64 # tail -1 /etc/lsb-release DISTRIB_DESCRIPTION="Ubuntu 12.04.1 LTS" # kvm --version QEMU emulator version 1.0 (qemu-kvm-1.0), Copyright (c) 2003-2008 Fabrice Bellard # libvirtd --version libvirtd (libvirt) 0.9.8

Guest

# tail -1 /etc/lsb-release DISTRIB_DESCRIPTION="Ubuntu 12.04.1 LTS" # uname -ri 3.2.0-29-virtual x86_64

current # of vCPUs : 1

maximum # of vCPUs : 2

current status

virsh # vcpucount ubuntu12-04-vm1 maximum      config         2 maximum      live           2 current      config         1 current      live           1 virsh # qemu-monitor-command ubuntu12-04-vm1 --hmp 'info cpus' * CPU #0: pc=0xffffffff8103bf6b (halted) thread_id=16145

add one vCPU

virsh # setvcpus ubuntu12-04-vm1 --count 2 –live

check vCPU info

virsh # vcpucount ubuntu12-04-vm1 maximum      config         2 maximum      live           2 current      config         1 current      live           2

virsh # qemu-monitor-command ubuntu12-04-vm1 --hmp 'info cpus' * CPU #0: pc=0xffffffff8103bf6b (halted) thread_id=16145

nnn , the vCPU I hot plugged does not appear on the VM.

on the VM

root@ubuntu12-04-vm1:~# ls /sys/devices/system/cpu/ cpu0     cpuidle     offline  possible  probe cpufreq  kernel_max  online   present   release

check VM’s log on the KVM host

# cat /var/log/libvirt/qemu/ubuntu12-04-vm1.log cpu hotplug not supported

cpu hotplug not supported..

Seen from “man kvm” , it describes that maxcpus specifies the maximum number of hotpluggable CPUs.

man kvm

-smp       n[,cores=cores][,threads=threads][,sockets=sockets][,maxcpus=maxcpus]           Simulate an SMP system with n CPUs. On the PC target, up to 255           CPUs are supported. On Sparc32 target, Linux limits the number of           usable CPUs to 4.  For the PC target, the number of cores per           socket, the number of threads per cores and the total number of           sockets can be specified. Missing values will be computed. If any           on the three values is given, the total number of CPUs n can be           omitted. maxcpus specifies the maximum number of hotpluggable CPUs.

Here is the command line parameter.

# cat /proc/16142/cmdline /usr/bin/kvm-S-Mpc-1.0-enable-kvm-m512-smp1,maxcpus=2,sockets=2,cores=1,threads=1-nameubuntu12-04-vm1-uuidf439b59e-2c1d-02b2-0cb9-fa71d5b189ed-nodefconfig-nodefaults-chardevsocket,id=charmonitor,path=/var/lib/libvirt/qemu/ubuntu12-04-vm1.monitor,server,nowait-monchardev=charmonitor,id=monitor,mode=control-rtcbase=utc-no-shutdown-drivefile=/var/disk1/images/ubuntu12-04-vm1.qcow2,if=none,id=drive-ide0-0-0,format=qcow2-deviceide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1-netdevtap,fd=23,id=hostnet0-devicevirtio-net-pci,netdev=hostnet0,id=net0,mac=xx:xx:xx:97:2d:78,bus=pci.0,addr=0x3-chardevpty,id=charserial0-deviceisa-serial,chardev=charserial0,id=serial0-usb-vnc127.0.0.1:3-vgacirrus-devicevirtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4

I need to look into this..