Re: [libvirt] [RFC PATCH v1 0/4] Add cpu hotplug support to libvirt.

It seems that libvirt is not cpu hotplug aware. Please refer to the following problem. 1. At first, we have 2 cpus. # cat /cgroup/cpuset/cpuset.cpus 0-1 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0-1 2. And we have a vm1 with following configuration. <cputune> <vcpupin vcpu='0' cpuset='1'/> <hypervisorpin cpuset='1'/> </cputune> 3. Offline cpu1. # echo 0 > /sys/devices/system/cpu/cpu1/online # cat /sys/devices/system/cpu/cpu1/online 0 # cat /cgroup/cpuset/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/lxc/cpuset.cpus 0 4. Online cpu1. # echo 1 > /sys/devices/system/cpu/cpu1/online # cat /sys/devices/system/cpu/cpu1/online 1 # cat /cgroup/cpuset/cpuset.cpus 0-1 # cat /cgroup/cpuset/libvirt/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/qemu/cpuset.cpus 0 # cat /cgroup/cpuset/libvirt/lxc/cpuset.cpus 0 Here，cgroup updated cpuset.cpus，but not for libvirt directory，and also qemu and lxc directory. vm1 cannot be started again. # virsh start vm1 error: Failed to start domain vm1 error: Unable to set cpuset.cpus: Permission denied And libvird gave the following errors. 2012-07-17 07:30:22.478+0000: 3118: error : qemuSetupCgroupVcpuPin:498 : Unable to set cpuset.cpus: Permission denied These patches resolves this problem by listening on the netlink for cpu hotplug event. When the netlink service gets the cpu hotplug event, it will attract the cpuid in the message, and add it into cpuset.cpus in: /cgroup/cpuset/libvirt /cgroup/cpuset/libvirt/qemu /cgroup/cpuset/libvirt/lxc