Re: [PATCH] Hotplug CPU prep V: x86 non-linear CPU numbers

[Alan Cox]

> APM is special: what it *really* wants to know is if only CPU 0 is
> online (this test will almost certainly fail miserably if the single
> online CPU is CPU 1, which previously wasn't possible).

It wants to know that only one CPU is running. Doesn't matter which.
APM as defined allows for SMP. APM in the real world doesn't work with
SMP but does work well with uniprocessors. People wanted an SMP kernel
on uniprocessor to do the right thing.

It may well be worth having an apm=on type option because some newer setups
especially those using SMM traps for everything seem to get it right

Alan