Looks like a good project -- new metrics like how much time a TCP session has been in different retransmit states should be useful for properly comprehending issues, and estimating speed up.

And it's a bunch of SystemTap scripts that trace send/receive/etc! Glad it isn't a kernel module, at least. :) So tracing send/receive does cost, which is covered in the README:

"The figure above shows Per-core CPU consumption of tcpdive is less than 10% while QPS is no significant influenced, which we believe is acceptable in most cases."

Actually, I'd say this was acceptable _because_ it is so clear in the README, and we can judge its usage beforehand. The overhead is actually pretty high, 2-10% CPU per core, but then that's what I'd expect for tracing send/receive using SystemTap. Again, by making it clear we can accept or not accept it beforehand and use accordingly.

eBPF should be making this type of tracing lower overhead...