Difference between qdisc and qdisc_sleeping, netdev_queue

What is the difference between qdisc and qdisc_sleeping? (in struct netdev_queue, file include/linux/netdevice.h) I've been trying to find the answer to this question for a while, but I didn't succeed. Does anyone knows why we need both pointers in netdev_queue? In addition, there are 2 different locks related to these 2 ptrs in include/net/sch_generic.h: qdisc_root_lock() and qdisc_root_sleeping_lock(). Why we need both? Thanks, -- Henrique Rodrigues