TCP initializer does not set NO_DELAY option. This has effect across all OS-es, but has especially bad effects on connection latency on Linux with kernel 3.14 and later which does additional aggressive throughput optimizations. This is why I am tagging this for Linux (Ubuntu LTS with updates will default to 3.16).

For nearly all openflow use cases openflow should operate in no-delay mode instead of throughput mode. This includes what openflow benchmarks call "throghput" as the actual throughput there is nowhere near what TCP means as throughput optimization. As a result of this option being not set:

1. OS Kernel will try to enqueue multiple frames to merge them into a single packet and wait until another frame is available instead of sending it immediately.

2. OS Kernel will not turn off additional throughput related optmizations (autocork in Linux) which are enabled by default.

This is a trivial one-liner, I will send a patch for it later today.