What 'onboot' option it is ? BTW, do you mean that ftrace backend is not necessary for libvirt now? Can it generate systemtap script automatically and load the module on boot time without users operation? We think adding multiple trace backends can provide more trace interfaces for the upper tool which is based on libvirt. Developer can chose more compatible trace scheme according to the actual situation with more flexibility . In the ways of usage by common user, ftrace is more lightweight ,more compact and easier. After all, writing systemTap script by users themselves and making it as an initscript is not convenient for them. Regards Yang Zhiyong