Performance

Dummynet is very efficient. Peak forwarding rate goes down by only a few percent compared to an equivalent ipfw config with no pipes.

Most operations are constant time per packet;

Other ops (pipe or queue scheduling) are logarithmic in the number of pipes/queues, i.e. still very efficient even with thousands of pipes/queues.

But beware, fetching state (ipfw show, ipfw pipe show) can be time consuming.