UDP套接字池会提高数据报传送成功率并提高效率吗？

Question

I am developing a UDP client module in Solaris using C, and there are 2 design modules:

(1) Create a socket, and send all messages through this socket. The receive thread only call recvfrom on this socket.

(2) Create a group of sockets. When sending message, select a socket randomly from the socket pool. The receive thread needs to call poll or select on a group of sockets.

When the throughput is low, I think the first design module is OK.

If the throughput is high, I am wondering whether the second design module can be better? Because it will dispatch messages to a group of sockets, and this maybe improve UDP datagram delivery successful rate and more efficient.

Answer 1

There's still only one network. You can have as many sockets, threads, whatever, as you like. The rate-determining step is the network. There is no point to this.

Answer 2

The question here primarily depends on how parallel the computer is (number of cores) and how parallel the algorithm is. Most likely your CPU cores are vastly faster than the network connection anyway and even one of them could easily overwhelm the connection. Thus on a typical system option (1) will give significantly better performance and lower drop rates.

This is because there is a significant overhead to using a UDP port on several threads or processes due to the internal locking the OS has to do to ensure the packets' contents are not multiplexed and corrupted, this causes a significant performance loss and significantly increased chance of packet loss where the kernel gives up waiting for other threads and just throws your pending packets away.

In the extreme case where your cores are very slow and your connection extremely fast (say a 500 core super computer with a 10 - 100Gbit fibre connection) option two could become more feasible, the locking would be less likely as the connection would be fast enough to keep many cores busy without them tripping over each other and locking often, this will -not- increase reliability (and may slightly decrease it) but might increase throughput depending on your architecture.

Overall in nearly every case I would suggest option 1, but if you really do have an extreme throughput situation you should look into other methods, however if you are writing software for this kind of system you would probably benefit from some more general training in massively parallel systems.

I hope this helps, if you have any queries please leave a comment.