NO_MIXED_MODE

[John Baldwin]

On Sunday 19 September 2004 04:39 pm, Scott Long wrote:
> Conrad J. Sabatier wrote:
> > On Sun, 19 Sep 2004 04:17:55 +0200, des at des.no (Dag-Erling Smørgrav)
> >
> > wrote:
> >>I just got an ASUS SK8N motherboard that has the problematic nForce 3
> >>chipset.  It runs 5.3 BETA4 fine, except you have to boot it in safe
> >>mode because the APIC only works properly in mixed mode, and GENERIC
> >>has the NO_MIXED_MODE option.  Took me quite a while to figure that
> >>out...
> >>
> >>Should we consider removing that option for 5.3-RELEASE?
> >
> > I'll second that motion.  I have the same chipset, and the same problem
> > with NO_MIXED_MODE.  I think we should err on the side of caution with
> > this one.
>
> Let's see what Peter, David, and John say about this.  My understanding
> is that mixed mode has a measurable performance impact, so we don't want
> to turn it on universally unless neccessary.  Maybe David knows of a
> BIOS upgrade that would help your motherboards.

You can toggle mixed mode via a loader tunable.  I'd add a note to the 
hardware notes suggesting that people with the specific motherboard break 
into the loader during install and do:

set hw.apic.mixed_mode=1

and then add an appropriate line to /boot/loader.conf after install.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org