> why not just call tcp_init_cwnd_reduction()? I deferred considering the ECN implications of doing so. The code to start PRR was based on tcp_enter_cwr()/tcp_init_cwnd_reduction(), save that both of these functions ensure a call to tcp_ecn_queue_cwr().
The upcoming patch set instead exports tcp_enter_cwr() and calls it, which sets CWR on ECN-capable connections. Consider CDG at the sender-side. The RFC 3168 Errata says that a receiver should: "First, reset ECE because of CWR Second, set ECE because of CE" Thus, in "good networks", setting CWR on a CDG backoff should not affect ECN signalling – we still get ECE from the receiver. It is conceivable that fringe scenarios of ECN in the forward path and losses in the ACK path creates a situation where CDG's backoff could inhibit some ECN signals from the receiver. That is, setting CWR will inhibit the signalling reliability of standard ECN in TCP. But we are arguably still in good faith since we have reduced the congestion window by some beta. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
