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
Tang Chen (4):
Add cpu hotplug handler for netlink service.
Register cpu hotplug netlink handler for libvirtd.
Register cpu hotplug netlink handler for qemu driver.
Register cpu hotplug netlink handler for lxc driver.
daemon/libvirtd.c | 11 +++
include/libvirt/virterror.h | 2 +
src/Makefile.am | 1 +
src/libvirt_private.syms | 5 +
src/lxc/lxc_driver.c | 8 ++
src/qemu/qemu_driver.c | 8 ++
src/util/cgroup.c | 6 +-
src/util/cgroup.h | 4 +
src/util/hotplug.c | 221 +++++++++++++++++++++++++++++++++++++++++++
src/util/hotplug.h | 32 +++++++
src/util/virterror.c | 3 +-
11 files changed, 297 insertions(+), 4 deletions(-)
create mode 100644 src/util/hotplug.c
create mode 100644 src/util/hotplug.h
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1.7.10.1