On Fri, 18 Apr 2003, Kevin Brown wrote:
> cbbrowne@cbbrowne.com wrote:
> > The "noapic" option seems a quasi-magical elixir for many sorts of
> > ailments.
> >
> > I upgraded a box to 2.4.20 and discovered that my NIC was no longer
> > properly recognized until I threw that option in. Others in my
> > office have /apparently/ the same hardware, and found they didn't
> > need the option.
> >
> > As a "fix," it certainly seems to fall into the
> > "snakeoil/superstition" category. While it often seems to have a
> > useful effect, I haven't located any actual explanations as to why
> > it should be expected to work.
>
> Well, when it comes to booting a computer, the placebo effect doesn't
> really exist. :-)
>
> Normally I'd agree that "noapic" sounds and smells like snakeoil. The
> problem is that it has observable and repeatable effects on some
> systems, and thus can't really be classified as snakeoil (much as one
> might like to!).
>
> Why should it be expected to work? I don't know...possibly because
> the APIC hardware is buggy (perhaps in very subtle ways) on some
> systems? Possibly because the APIC driver is subtlely incompatible
> with certain APIC hardware? Possibly because the APIC driver has
> certain subtle bugs that only manifest themselves on certain
> motherboards with certain peripheral devices?
>
> Whatever the reason, the "noapic" option *does* work on certain
> systems, so it unfortunately isn't something that can be dismissed as
> mere superstition -- the computer isn't being asked its opinion of its
> own health here, nor does it "know" that it should get "well" when
> given different boot options. No "placebo effect" involved, just
> repeatable observation (that the observation isn't terribly repeatable
> *across* systems does not diminish the validity of the observation).
Just to add to this, on some of the first SMP systems I messed with there
was a setting for some SMP version of 1.1 or 1.4, and using 1.1 resulted
in an unstable box for me. 1.4 fixed all the issues. SMP on Intel is a
wild ride, and no two motherboards are equivalent. I've had good luck
with Supermicro and Intel SMP motherboards, although both have needed BIOS
updates at times.
