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There is one important feature missing the NuttX TCP that can help when there is no write buffering: Without write buffering send() will not return until the transfer has been ACKed by the recipient. But under RFC 1122, the host need not ACK each packet immediately; the host may wait for 500 MS before ACKing. This combination can cause very slow performance when small, non-buffered transfers are made to an RFC 1122 client. However, the RFC 1122 must ACK at least every second (odd) packet so sequences of packets with write buffering enabled do not suffer from this problem.

Update:  RFC 1122 support was added to the NuttX TCP stack with commit 66ef6d143a627738ad7f3ce1c065f9b1f3f303b0 in December of 2019.  That, however, has no impact on transmitted packet performance; write buffering is still recommended.

TCPBlaster

I created a new test application at apps/examples/tcpblaster to measure TCP performance and collected some data for the configuration that happens to be on my desk. The tcpblaster test gives you the read and write transfer rates in Kb/sec (I won't mention the numbers because I don't believe they would translate any other setup and, hence, would be misleading).

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