Giant and MPSAFE

[Kris Kennaway]

On Sun, Oct 17, 2004 at 12:38:04PM +0100, Ben Paley wrote:
> Hello,
> 
> bash-2.05b$ uname -a
> FreeBSD potato.hogsedge.net 5.3-BETA5 FreeBSD 5.3-BETA5 #0: Mon Sep 20 
> 07:49:52 BST 2004     root at potato.hogsedge.net:/usr/obj/usr/src/sys/POTATO  
> i386
> 
> I've just noticed a nasty looking message at boot:
> 
> WARNING: debug.mpsafenet forced to 0 as aio requires Giant
> WARNING: MPSAFE network stack disabled, expect reduced performance.
> 
> And then subsequently there are a good few references to things being (from 
> memory)
> 
> [GIANT LOCKED]
> 
> Anyone have any idea what this is about, and if it's actually bad, and how I 
> can sort it out?

Some subsystems have not yet been modified so they take advantage of
multiple processors.  aio is one of them, and because it interlinks
with the network subsystem, if you have it in your kernel you can't
make use of smp in the entire network stack.

It's unlikely that you really need aio since it's still experimental
code, so you can just compile it out of your kernel.

Kris
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