aio info

Maxim Dounin mdounin at
Mon May 9 15:21:49 MSD 2011


On Mon, May 09, 2011 at 09:33:18AM +0000, Richard Kearsley wrote:

> Running nginx on freebsd 8.2 with 16 workers and aio on, when the server encounters heavy writes, all processes are in D state
> Aio queue is way below system/process limit
> A request for small file (said file will be in fs buffer/cache) every second varies wildly from 1ms to over 1s
> >From man ps:
> D       Marks a process in disk (or other short term, uninter-ruptible) wait.
> What's causing the lock?

You may want to look at WCHAN instead, it should contain more 

Please note that AIO interface only allows to do async reads, but 
open()/stat()/... are still blocking.  This may be a problem if 
you've run out of vnodes (sysctl kern.maxvnodes) or there are 
other reasons NAMEI lookups can't be effectively cached by OS.

Maxim Dounin

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