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aio_queue_async_request: too many in flight for proc: 16

Lateley I've been seeing the following on this MacOS 10.6.4 (xnu-1504.7.4):
   aio_queue_async_request(): too many in flight for proc: 16.
This is logged over and over again to the kernel log. The messages stem from bsd/kern/kern_aio.c, but I suspect the "rude" application doing this might be VirtualBox. That's the toughest application on this box anyway and I noticed quite a few (new) messages when VirtualBox is running. And since the VM in question was running suspiciously slow, I'm tempted to tune these limits. How about:
# sysctl -w kern.aiomax=128 kern.aioprocmax=32 kern.aiothreads=8
kern.aiomax: 90 -> 128
kern.aioprocmax: 16 -> 32
kern.aiothreads: 4 -> 8
I haven't done any tests yet, so let's wait and see if it helps - or breaks :-))

Update: Even with MacOS 10.6.7 (1504.9.37), /etc/rc.local is still being parsed during bootup, so we can put these commands in there! :-)


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Jaakko Linnosaari on :

Hmm, why not put those modifications in /etc/sysctl.conf?

Christian on :

Good idea :-) I did not know that MacOS X honors sysctl.conf(5), but apparently it does. Thanks!

Gabriel on :

Hey Christian, sorry for opening up an old topic but I just ran into this myself, was wondering how those adjustments worked for you.

Christian on :

Sorry for not replying sooner: I'm on MacOS 10.7.2 now and haven't touched these parameters a long time ago, meaning they're all on their default value here. The message is still there, but appearing less often than in 10.6 - at least not often enough for me to bother :-) I'll try to keep an eye on it and will update the blog entry in a while, if I don't forget :-)

Robert on :

I've been getting this a lot. 3 times just today! Usually it's just once a month or so. Snow Leopard 10.6.8 and VirtualBox 4.1.2 running Fedora 15 LXDE

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