Re: aio

[Dan Kegel <dank@kegel.com>]

Ingo Molnar wrote:

> it's not a fair comparison. The system was set up to not exhibit any async
> IO load. So a pure, atomic sendfile() outperformed TUX slightly, where TUX
> did something slightly more complex (and more RFC-conform as well - see
> Date: caching in X12 for example). Not something i'd call a proof - this
> simply works around the async IO interface. (which RT-signal driven,
> fasync-helped async IO interface, as phttpd has proven, is not only hard
> to program and is unrobust, it also performs *very badly*.)

Proper wrapper code can make them (almost) easy to program with.
See http://www.kegel.com/dkftpbench/doc/Poller_sigio.html for an example
of a wrapper that automatically handles the fallback to poll() on overflow.
Using this wrapper I wrote ftp clients and servers which use a thin wrapper
api that lets the user choose from select, poll, /dev/poll, kqueue/kevent, and RT signals
at runtime.

That said, I think that using the RT signal queue is just plain the
wrong way to go, and I can't wait for better approaches to make it
into the standard kernel someday.

- Dan