Tom Tom - 6 months ago 114
Linux Question

Disable TCP Delayed ACKs

I have an application that receives relatively sparse traffic over TCP with no application-level responses. I believe the TCP stack is sending delayed ACKs (based on glancing at a network packet capture). What is the recommended way to disable delayed-ACK in the network stack for a single socket? I've looked at

TCP_QUICKACK
, but it seems that the stack will change it under my feet anyways.

This is running on a Linux 2.6 kernel, and I am not worried about portability.

Answer

You could setsockopt(sockfd, IPPROTO_TCP, TCP_QUICKACK, (int[]){1}, sizeof(int)) after every recv you perform. It appears that TCP_QUICKACK is only reset when there is data being sent or received; if you're not sending any data, then it will only get reset when you receive data, in which case you can simply set it again.

You can check this in the 14th field of /proc/net/tcp; if it is not 1, ACKs should be sent immediately... if I'm reading the TCP code correctly. (I'm not an expert at this either.)

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