vfs.aio tuning question

Louis LeBlanc freebsd at keyslapper.org
Thu Nov 6 11:27:46 PST 2003

Couldn't find any real explanation of these parameters online, but I
noticed they appear to have disappeared in 4.8.

I have a 4.6 system that shows the following parameters when sysctl -a
is executed:

vfs.aio.max_aio_per_proc: 72
vfs.aio.max_aio_queue_per_proc: 1024
vfs.aio.max_aio_procs: 32
vfs.aio.num_aio_procs: 0
vfs.aio.num_queue_count: 0
vfs.aio.max_aio_queue: 1024
vfs.aio.target_aio_procs: 4
vfs.aio.max_buf_aio: 72
vfs.aio.num_buf_aio: 0
vfs.aio.aiod_lifetime: 3000
vfs.aio.aiod_timeout: 1000

Now, I'm pretty sure these have something to do with asynchronous I/O,
and I'm under the impression this is a bad thing to use.  It appears
this 4.6.2-RELEASE system is using it, but I don't know how to verify
it or how to be sure it's not going to wreck something.

If possible, I'd like someone to point me to a reference that
describes the async features in some detail and particularly these
parameters.  Also, are they really gone from 4.8 or do they have to be
'turned on' somehow - and when is this an acceptable configuration?

Thanks a lot folks.

Louis LeBlanc               leblanc at keyslapper.org
Fully Funded Hobbyist, KeySlapper Extrordinaire :)
http://www.keyslapper.org                     Ô¿Ô¬

All Finagle Laws may be bypassed by learning the simple art of doing
without thinking.

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