CentOS 7 blockdevice performance problems with virtio

Hi all

We have detected a performance problem in CentOS 7 and want to know if it is a known problem. I cant find anything about it. So i hope someone has a hint for me.

The Centos7 image from ONE includes a older Kernel (3.10.0-123.el7.x86_64). With that system, i get up to 600MB/sec inside the VM.
When i do a system update, including kernel 3.10.0-229.7.2.el7.x86_64 - i get only 300MB/sec.

Also the CPU usage of the qemu-kvm process is much higher(+100%) with the updated System if i do some harder I/O jobs.

We use OpenNebula with StorPool.

best regards,