It's ACK aggregation limit is append count based, while the TCP data segment aggregation is length based. Unless the network driver sets these two limits, its an NO-OP.
- Set TCP ACK append limit to 1, i.e. aggregate 2 ACKs at most. Aggregate anything more than 2 hurts TCP sending performance in hyperv. This significantly improves the TCP sending performance when the number of concurrent connetion is low (2~8). And greatly stabilize the TCP sending performance in other cases.
- Set TCP data segments length limit to 37500. Without this limitation, hn(4) could aggregate ~45 TCP data segments for each connection (even at 64 or more connections) before dispatching them to socket code; large aggregation slows down ACK sending and eventually hurts/destabilizes TCP reception performance. This setting stabilizes and improves TCP reception performance for >4 concurrent connections significantly.
Make them sysctls so they could be adjusted.