A number of years ago I tested the Linux ECN support and found that so much of the internet became inaccessible that keeping it turned off was the only sensible things to do. A few days ago while working on ingress traffic shaping I decided to try again. With ingress traffic shaping the only way to get a host to send slower is to drop packets forcing them to be re-transmitted. ECN could help alleviate waste by allowing a host to signal that packets are coming to fast without dropping packets that have already arrived. Unfortunately it did not take very long to learn that ECN is still unusable due to the large number of devices which will not pass traffic from ECN enabled hosts. My home DSL modem was one of them. Maybe someday ECN will work and enable smarter traffic control but I won't be holding my breath.