one two-directed tcp socket OR two one-directed? (linux, high volume, low latency)
- by osgx
Hello
I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets?
The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe).
The benefit of 2 uni-directed connections come from linux:
http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847
3847/*
3848 * TCP receive function for the ESTABLISHED state.
3849 *
3850 * It is split into a fast path and a slow path. The fast path is
3851 * disabled when:
...
3859 * - Data is sent in both directions. Fast path only supports pure senders
3860 * or pure receivers (this means either the sequence number or the ack
3861 * value must stay constant)
...
3863 *
3864 * When these conditions are not satisfied it drops into a standard
3865 * receive procedure patterned after RFC793 to handle all cases.
3866 * The first three cases are guaranteed by proper pred_flags setting,
3867 * the rest is checked inline. Fast processing is turned on in
3868 * tcp_data_queue when everything is OK.
All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive
