1.add read only file /sys/fs/cgroup/cpu/cpu.rt_runtime_borrow_us and operating functions
2.in the cgroup mechanism, the CPU utilization of lower priority cgroup in each period can't increase if the higher priority cgroup keeps busy.
we fix this bug, see my google drive for details.
3.some time one cgroup's rt_time will overflow, so that the cgroup can't scheduled for a very long time.
we just check rt_time and correct it when overflow until find out the root cause.