Boosting Socket Performance on Linux

Cop writes "The Sockets API lets you develop client and server applications that can communicate across a local network or across the world via the Internet. Like any API, you can use the Sockets API in ways that promote high performance -- or inhibit it. This article explores four ways to use the Sockets API to squeeze the greatest performance out your application and to tune the GNU/Linux® environment to achieve the best results."

Comments

Re:Code Portability

[complexmath]

There was a Boost library in the works to encapsulate all of this rather nicely, but I'm not sure if it ever made it out of beta. ACE is another option, though that tends to be overkill for some projects. I rolled my own class wrapper around this stuff, but then I enjoy library programming.

Nagle's algorithm

[Jeremi]

For an application where I want both low latency AND high bandwidth, it's not enough to leave Nagle's algorithm on or off. If I leave it on, I'll get increased bandwidth, but >200ms latency due to the Nagle delay. If I leave it off, I get low latency, but the computer will (typically?) send out one network packet per send() call, which means inefficient use of bandwidth unless the calling code is very careful to call send() only with large amounts of data per call.

To get around the above problems, I came up with the following scheme: Leave Nagle's algorithm enabled, but create a FlushSocket() function that merely disables Nagle on the socket, then calls send() on the socket with a 0-byte buffer, then enables Nagle again. This apparently forces the TCP stack to immediately send any data that it may have accumulated in its Nagle-buffer. Therefore the only thing the calling code has to remember to do is to call FlushSocket() whenever it has called send() one or more times and doesn't think it will be sending any more data any time soon.

The above technique seems to work pretty well under Linux, Windows, and OS/X (and is more portable than Linux-specific flags like TCP_CORK, etc), but I haven't seen it documented anywhere. Is that simply an oversight, or is there some nasty downside to this technique that I'm overlooking?