Fundamentally if we want things to get better we have to remove unnecessary serialization. It is entirely too easy to sleep when cleaning up a networking subsystem and create long hold times on net_mutex for no particular reasons.
What probably makes sense to do is to add the concept of a non-serialized pernet_operation. And then work through the networking stack converting all of the pernet_operations. That should allow network namespace exits to overlap while they clean up, and it should allow the net_mutex to be dropped at the same point we drop rtnl_lock in cleanup_net. It might be a touch tricky during the transition period to take advantage of an early drop of net_mutex, but that is where I would start. Once net_mutex is no longer used to serialize initialization/cleanup methods for a network namespace. We can look at other bottlenecks. Eric
