When doing tcp rx testing, I saw a lot of retransmission because of the
delayed ACK. Our current delayed ACK algorithm does not comply with
what RFC 1122 suggests.
As described in RFC 1122, a host may delay sending an ACK response by up
to 500 ms. Additionally, with a stream of full-sized incoming segments,
ACK responses must be sent for every second segment.
=== Before ===
[asias@hjpc pingpong]$ go run client-rxrx.go
Bytes Sent(MiB): 100
Total Time(Secs): 322.620879376
Bandwidth(MiB/Sec): 0.30996133974160595
78 2.412385 192.168.66.100 -> 192.168.66.123 TCP 32174 37672 > 10000
[ACK] Seq=2149425323 Ack=1000001 Win=229 Len=32120
79 2.612985 192.168.66.100 -> 192.168.66.123 TCP 1514 [TCP Retransmission]
37672 > 10000 [ACK] Seq=2149425323 Ack=1000001 Win=229 Len=1460
80 2.613131 192.168.66.123 -> 192.168.66.100 TCP 54 10000 > 37672
[ACK] Seq=1000001 Ack=2149457443 Win=29200 Len=0
=== After ===
[asias@hjpc pingpong]$ go run client-rxrx.go
Bytes Sent(MiB): 100
Total Time(Secs): 0.244951095
Bandwidth(MiB/Sec): 408.2447559583271
No retransmission is seen.
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