Experimental patch to support disk AIO on FreeBSD and Linux.

./configure --with-file-aio ...

nginx.conf:

location / {
aio on;
output_buffers 1 128k;
}

----------

Linux: at least 2.6.22 kernel is required. Probably, you need to enable
directio as well (otherwise kernel may fall back to synchronous IO,
however, I'm not sure):

location / {
aio on;
directio 1;
output_buffers 1 128k;
}

----------

FreeBSD: should work on 4+, however, 7.x is preferable: on 6.x the network
subsystem is GiantLock'ed if AIO is used.

Kernel must support AIO:

options VFS_AIO
or
kldload aio

Probably you need to tune the sysctls:

vfs.aio.max_aio_queue (default) 1024
vfs.aio.max_aio_queue_per_proc 256
vfs.aio.max_aio_per_proc 32
vfs.aio.max_aio_procs 32

You may diagnose load using

vfs.aio.num_queue_count
vfs.aio.num_aio_procs

If kernel AIO queue overflows then nginx fall back to synchronous IO.


--
Igor Sysoev
http://sysoev.ru/en/