Disable TCP Delayed ACKs

Question

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 glanci

Answer 1

The accepted answer has a bug, it should be

flags = 0;
flglen = sizeof(flags);
setsockopt(sfd, SOL_TCP, TCP_QUICKACK, &flags, flglen)

(SOL_TCP, not IPPROTO_TCP)

Post here in case someone need it.

As @damolp suggested, it is not a bug. Keep it here for record.

Answer 2

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 14^th 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.)

Answer 3

I believe using the setsockopt() function you can use the TCP_NODELAY which will disable the Nagle algorithm.

Edit Found a link: http://www.ibm.com/developerworks/linux/library/l-hisock.html

Edit 2 Tom is correct. Nagle does not affect Delayed ACKs.