[libvirt] libvirt qemu cgroup problem

I want to use the cgroup with libvirt+qemu. The VM runs well. But the libvirt report error, here is the libvirt debug info: 2012-07-19 09:40:10.726+0000: 32341: debug : virCgroupNew:603 : New group / 2012-07-19 09:40:10.726+0000: 32341: info : qemudStartup:597 : Unable to create cgroup for driver: No such device or address 2012-07-19 09:40:10.726+0000: 32341: debug : virLockManagerNopInit:35 : version=1000000 configFile=(null) flags=0 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'cpu' 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'cpuacct' 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'cpuset' 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'memory' 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'devices' 2012-07-19 09:40:10.726+0000: 32341: info : qemudLoadDriverConfig:332 : Configured cgroup controller 'blkio' I can't find the /sys/fs/cgroup dir or any other dir? virsh blkiotune test error: Unable to get blkio parameters error: Requested operation is not valid: blkio cgroup isn't mounted ------ thank you.