On Sun, Aug 21, 2011 at 01:10:05AM +0400, Lev Serebryakov wrote:

i am working on the following now: - routing daemons and the like still work as usual, adding and modifying routes with the standard mechanisms (routing sockets etc.) - the kernel updates its own forwarding tables (FIB) as usual

But: - a netmap client (userspace) listens for FIB updates on a routing socket, and builds its own copy of the FIB in userspace (call it uFIB) - the same process sets interfaces in netmap mode, and uses the uFIB to do forwarding, injecting back into the kernel those packets that have a local destination.

essentially, the driver in netmap mode is way more efficient and this offsets the cost of the few syscalls. As an example, currently with netmap one core can forward packets between interfaces at a rate between 3 and 10 Mpps depending on the amount of processing on the packet, and there are significant optimizations that are still possible especially at the lower speeds (if 3 Mpps can be called so)

Nothing prevents, of course, that kernel subsystems use the interface directly in netmap mode. But i think that now that we have the option, it makes sense to spend some time to experiment with newer solutions (FIB data structures, firewalls, memory aligment, possibly even tcp buffer management) in userspace and then move stuff back into the kernel once we have a good solution.

i am using it for prototyping and testing subsystems in userspace, whether it makes sense to move them depends on the performance we manage to get.

cheers luigi