On 09/03/2012 08:06 AM, Tang Chen wrote:
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
Hi,
this approach requires that libvirtd keeps running through the entire
lifecycle of a guest. That is something that cannot be safely assumed
and therefore hotplug events can be missed.
That means that libvirt must synchronize the hypervisors cpusets with
the host's current CPU states. You could do that for instance when
registering the callback.
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Mit freundlichen Grüßen/Kind Regards
Viktor Mihajlovski
IBM Deutschland Research & Development GmbH
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