ca09d7728b
too coarse grained to be useful and the default value significantly degrades TCP performance on moderate to high bandwidth-delay product paths with non-zero loss (e.g. 5+Mbps connections across the public Internet often suffer). Replace the outgoing mechanism with an individual per-queue limit based on the number of MSS segments that fit into the socket's receive buffer. This should strike a good balance between performance and the potential for resource exhaustion when FreeBSD is acting as a TCP receiver. With socket buffer autotuning (which is enabled by default), the reassembly queue tracks the socket buffer and benefits too. As the XXX comment suggests, my testing uncovered some unexpected behaviour which requires further investigation. By using so->so_rcv.sb_hiwat instead of sbspace(&so->so_rcv), we allow more segments to be held across both the socket receive buffer and reassembly queue than we probably should. The tradeoff is better performance in at least one common scenario, versus a devious sender's ability to consume more resources on a FreeBSD receiver. Sponsored by: FreeBSD Foundation Reviewed by: andre, gnn, rpaulo MFC after: 2 weeks