[libvirt-users] virsh hangs when backup jobs run on the kvm host

Hi, Has anyone met the same problem that virsh hangs when there are some backup jobs running on the kvm host? I use dirty bitmap supported by qemu to do backups every 6 minitues. About a few hours later, I ran 'virsh list', It hung. Then I stopped the backup jobs ，nothing was getting better. I had checked the libvirt logs ，but found nothing useful . Maybe the high I/O caused the problem? or there are connection number limits when using virsh, because I use virsh to check the backup jobs are still running every 10 seconds? My os version is ' Ubuntu 12.04 LTS Release: 12.04 Codename: precise,Linux version 4.1.0-generic (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) ) #1 SMP Wed Nov 9 02:04:23 CST 2016'. KVM version is 'QEMU emulator version 2.7.1(Debian 1:2.7+dfsg-3)'. Hoping for you reply. Thanks!