This new feature will help live migration converge when the guest is dirtying pages too fast for the network throughput.

The performance team is using a script like this:

# cat migrated_cgroup.sh
# Enter guest name $1
#
# Try for 120 seconds with 10 percent of 1-cpu
echo 10000 > /cgroup/cpu/libvirt/qemu/$1/vcpu0/cpu.cfs_quota_us
echo 10000 > /cgroup/cpu/libvirt/qemu/$1/vcpu1/cpu.cfs_quota_us
sleep 120
# Try for 2 minutes with 1% of the cpu of 1-cpu
echo 1000 > /cgroup/cpu/libvirt/qemu/$1/vcpu0/cpu.cfs_quota_us
echo 1000 > /cgroup/cpu/libvirt/qemu/$1/vcpu1/cpu.cfs_quota_us
sleep 120
# Increase the period to then reduce to .1% of 1-cpu.
echo 1000000 > /cgroup/cpu/libvirt/qemu/$1/vcpu0/cpu.cfs_period_us
echo 1000000 > /cgroup/cpu/libvirt/qemu/$1/vcpu1/cpu.cfs_period_us
echo 1000 > /cgroup/cpu/libvirt/qemu/$1/vcpu0/cpu.cfs_quota_us
echo 1000 > /cgroup/cpu/libvirt/qemu/$1/vcpu1/cpu.cfs_quota_us

This logic should be refined and put into libvirt so it's automatic for the customer.