Loopback ACK delays cause Cubic slowdowns

The first investigation of loopback performance focused on the randomness of the RTT measurements on loopback, and the fix for BBR was to not make congestion control decisions based on delays if the RTT were small. After that, the results “looked good”, although there was quite a bit of variability in the results. The tests were made by sending 1GB of data. Looking at traces, it seemed that many…